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Chapter 1. Welcome to Design Patterns
Table of Contents Chapter 1. Welcome to Design Patterns....................................................... 1 Section 1.1. It started with a simple SimUDuck app....................................................................................................................... 2 Section 1.2. But now we need the ducks to FLY............................................................................................................................. 3 Section 1.3. But something went horribly wrong........................................................................................................................... 4 Section 1.4. Joe thinks about inheritance....................................................................................................................................... 5 Section 1.5. Sharpen your pencil..................................................................................................................................................... 5 Section 1.6. How about an interface?............................................................................................................................................. 6 Section 1.7. What would you do if you were Joe?........................................................................................................................... 7 Section 1.8. The one constant in software development................................................................................................................ 8 Section 1.9. Sharpen your pencil.................................................................................................................................................... 8 Section 1.10. Zeroing in on the problem......................................................................................................................................... 9 Section 1.11. Separating what changes from what stays the same............................................................................................... 10 Section 1.12. Designing the Duck Behaviors.................................................................................................................................. 11 Section 1.13. Implementing the Duck Behaviors.......................................................................................................................... 13 Section 1.14. There are no Dumb Questions................................................................................................................................. 14 Section 1.15. Sharpen your pencil.................................................................................................................................................. 14 Section 1.16. Integrating the Duck Behavior................................................................................................................................. 15 Section 1.17. More Integration...................................................................................................................................................... 16 Section 1.18. Testing the Duck code.............................................................................................................................................. 18 Section 1.19. Setting behavior dynamically.................................................................................................................................. 20 Section 1.20. The Big Picture on encapsulated behaviors............................................................................................................ 22 Section 1.21. HAS-A can be better than IS-A................................................................................................................................ 23 Section 1.22. Speaking of Design Patterns................................................................................................................................... 24 Section 1.23. Design Puzzle........................................................................................................................................................... 25 Section 1.24. Overheard at the local diner.................................................................................................................................... 26 Section 1.25. Overheard in the next cubicle.................................................................................................................................. 27 Section 1.26. The power of a shared pattern vocabulary............................................................................................................. 28 Section 1.27. How do I use Design Patterns?............................................................................................................................... 29 Section 1.28. There are no Dumb Questions................................................................................................................................ 29 Section 1.29. Skeptical Developer-Friendly Patterns Guru......................................................................................................... 30 Section 1.30. Tools for your Design Toolbox................................................................................................................................ 32 Section 1.31. Design Puzzle Solution............................................................................................................................................ 34 Section 1.32. Solutions.................................................................................................................................................................. 35
Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Intro to Design Patterns
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 1. Welcome to Design Patterns
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 1. Welcome to Design Patterns
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 1. Welcome to Design Patterns
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[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 1. Welcome to Design Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 2. Keeping your Objects in the know
Table of Contents Chapter 2. Keeping your Objects in the know.............................................. 1 Section 2.1. The Weather Monitoring application overview.......................................................................................................... 3 Section 2.2. Unpacking the WeatherData class.............................................................................................................................. 4 Section 2.3. What do we know so far ?........................................................................................................................................... 5 Section 2.4. Taking a first, misguided SWAG at the Weather Station........................................................................................... 6 Section 2.5. Sharpen your pencil.................................................................................................................................................... 6 Section 2.6. What's wrong with our implementation?................................................................................................................... 7 Section 2.7. Meet the Observer Pattern.......................................................................................................................................... 8 Section 2.8. Publishers + Subscribers = Observer Pattern............................................................................................................ 9 Section 2.9. A day in the life of the Observer Pattern................................................................................................................... 10 Section 2.10. Five minute drama: a subject for observation........................................................................................................ 12 Section 2.11. Two weeks later........................................................................................................................................................ 14 Section 2.12. The Observer Pattern defined.................................................................................................................................. 15 Section 2.13. The Observer Pattern defined: the class diagram................................................................................................... 16 Section 2.14. The power of Loose Coupling.................................................................................................................................. 17 Section 2.15. Sharpen your pencil................................................................................................................................................. 18 Section 2.16. Cubicle conversation................................................................................................................................................ 19 Section 2.17. Designing the Weather Station............................................................................................................................... 20 Section 2.18. Implementing the Weather Station......................................................................................................................... 21 Section 2.19. Implementing the Subject interface in WeatherData............................................................................................. 22 Section 2.20. Now, let's build those display elements................................................................................................................. 23 Section 2.21. There are no Dumb Questions................................................................................................................................ 23 Section 2.22. Power up the Weather Station................................................................................................................................ 24 Section 2.23. Sharpen your pencil................................................................................................................................................ 25 Section 2.24. Using Java's built-in Observer Pattern.................................................................................................................. 28 Section 2.25. How Java's built-in Observer Pattern works.......................................................................................................... 29 Section 2.26. Reworking the Weather Station with the built-in support..................................................................................... 31 Section 2.27. Now, let's rework the CurrentConditionsDisplay................................................................................................... 32 Section 2.28. Exercise: Code Magnets.......................................................................................................................................... 33 Section 2.29. Running the new code............................................................................................................................................ 34 Section 2.30. The dark side of java.util.Observable..................................................................................................................... 35 Section 2.31. Other places you'll find the Observer Pattern in the JDK...................................................................................... 36 Section 2.32. And the code............................................................................................................................................................ 37 Section 2.33. Tools for your Design Toolbox................................................................................................................................ 38 Section 2.34. Exercise: Design Principle Challenge..................................................................................................................... 39 Section 2.35. Exercise solutions: Design Principle Challenge...................................................................................................... 41 Section 2.36. Code Magnets: Exercise solutions.......................................................................................................................... 42
Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 21
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 23
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know
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[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 29
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 30
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 31
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 33
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 2. Keeping your Objects in the know Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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3 the DecoratorPattern
g Decorating
h
Objects g
I used to think real men subclassed everything. That was until I learned the power of extension at runtime, rather than at compile time. Now look at me!
Just call this chapter “Design Eye for the Inheritance Guy.” We’ll re-examine the typical overuse of inheritance and you’ll learn how to decorate your classes at runtime using a form of object composition. Why? Once you know the techniques of decorating, you’ll be able to give your (or someone else’s) objects new responsibilities without making any code changes to the underlying classes.
this is a new chapter
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79
the starbuzz story
Welcome to Starbuzz Coffee Starbuzz Coffee has made a name for itself as the fastest growing coffee shop around. If you’ve seen one on your local corner, look across the street; you’ll see another one. Because they’ve grown so quickly, they’re scrambling to update their ordering systems to match their beverage offerings. When they first went into business they designed their classes like this...
stract class, Beverage is an abbe verages subclassed by all ff ee shop. offered in the co
The description instance variable is set in each subclass and holds a description of the beverage, like “Most Excellent Dark Roast”. The getDescription() method returns the description.
Beverage description
The cost() method is abstract; subclassses need to define their own implementation.
getDescription() cost() // Other useful methods...
DarkRoast
HouseBlend cost()
cost()
Decaf cost()
Espresso cost()
Each subclass implements cost() to return the cost of the beverage.
80
Chapter 3
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the decorator pattern
In addition to your coffee, you can also ask for several condiments like steamed milk, soy, and mocha (otherwise known as chocolate), and have it all topped off with whipped milk. Starbuzz charges a bit for each of these, so they really need to get them built into their order system. Here’s their first attempt... Beverage description getDescription() cost() // Other useful methods...
DarkRoastWithSteamedMilk andMocha
HouseBlendWithSteamedMilk andMocha HouseBlendWithSteamedMilk cost() andCaramel HouseBlendWithWhipandMocha
cost()
cost()
cost()
DecafWithSteamedMilk andCaramel
DarkRoastWithSteamedMilk andCaramel
cost()
HouseBlendWithMocha cost() HouseBlendWithSoyandMocha
EspressoWithSteamedMilk andMocha
DecafWithSteamedMilk andMocha
cost()
EspressoWithSteamedMilk andCaramel
EspressoWithWhipandMocha
cost()
DecafWithWhipandMocha
cost() DarkRoastWithWhipandMocha
cost()
cost()
HouseBlendWithSteamedMilk andSoycost() cost()
HouseBlendWithWhip
cost()
cost()
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DarkRoastWithSteamedMilk andSoy
HouseBlendWithSteamedMilk cost() cost()
cost() DarkRoastWithSteamedMilk
cost() HouseBlendWithSteamedMilk andWhip
cost() HouseBlendWithWhipandSoy
cost()
EspressoWithSteamedMilk DecafWithSoy andSoy DecafWithSteamedMilk cost() andSoy EspressoWithSteamedMilk cost()
DarkRoastWithSoy cost() DecafWithSteamedMilk cost() DecafWithSoyandMocha DarkRoastWithSoy DarkRoastWithSoyandMocha cost() DecafWithSoy cost() DecafWithSoyandMocha cost() EspressoWhip cost() cost()
cost()
DecafWithWhip cost()
DarkRoastWithWhip
cost()
cost()
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cost()
EspressoWithMocha
cost() DecafWithMocha
cost()
DarkRoastWithMocha
cost() cost()
cost()
mputes the Each cost method coalo ng with the cost of the coffee the order. other condiments in
Whoa! Can you say “class explosion?”
you are here 4
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81
violating design principles
A
brain power
It’s pretty obvious that Starbuzz has created a maintenance nightmare for themselves. What happens when the price of milk goes up? What do they do when they add a new caramel topping? Thinking beyond the maintenance problem, which of the design principles that we’ve covered so far are they violating? Hint: they’re violating two of them in a big way! This is stupid; why do we need all these classes? Can’t we just use instance variables and inheritance in the superclass to keep track of the condiments?
Well, let’s give it a try. Let’s start with the Beverage base class and add instance variables to represent whether or not each beverage has milk, soy, mocha and whip...
Beverage
New boolean values for each condiment.
description milk soy mocha whip
Now we’ll implement cost() in Beverage (instead of keeping it abstract), so that it can calculate the costs associated with the condiments for a particular beverage instance. Subclasses will still override cost(), but they will also invoke the super version so that they can calculate the total cost of the basic beverage plus the costs of the added condiments.
getDescription() cost() hasMilk() setMilk() hasSoy() setSoy() hasMocha() setMocha() hasWhip() setWhip()
e boolean These get and setndthiments. values for the co
// Other useful methods..
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Now let’s add in the subclasses, one for each beverage on the menu:
e st() will calculate th The superclass coth ile wh , condiments costs for all of ste() in the subclasses the overridden cofunctionality to will extend that that specific include costs for beverage type. needs to compute Each cost() methobedverage and then the cost of the ents by calling the add in the condim tation of cost(). superclass implemen
getDescription() cost() hasMilk() setMilk() hasSoy() setSoy() hasMocha() setMocha() hasWhip() setWhip() // Other useful methods..
DarkRoast
HouseBlend
Decaf
cost()
cost()
Sharpen your pencil
cost()
Espresso cost()
Write the cost( ) methods for the following classes (pseudo-Java is okay):
public class Beverage { public double cost() {
public class DarkRoast extends Beverage { public DarkRoast() { description = “Most Excellent Dark Roast”; } public double cost() {
}
}
}
}
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impact of change
See, five classes total. This is definitely the way to go.
I’m not so sure; I can see some potential problems with this approach by thinking about how the design might need to change in the future.
Sharpen your pencil What requirements or other factors might change that will impact this design?
Price changes for condiments will force us to alter existing code. New condiments will force us to add new methods and alter the cost method in the superclass. We may have new beverages. For some of these beverages (iced tea?), the condiments may not be appropriate, yet the Tea subclass will still inherit methods like hasWhip(). What if a customer wants a double mocha?
rn:
Your tu
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aw in this is s e As w pter 1, idea! Cha ery bad av
the decorator pattern
Master and Student... Master: Grasshopper, it has been some time since our last meeting. Have you been deep in meditation on inheritance? Student: Yes, Master. While inheritance is powerful, I have learned that it doesn’t always lead to the most flexible or maintainable designs. Master: Ah yes, you have made some progress. So, tell me my student, how then will you achieve reuse if not through inheritance? Student: Master, I have learned there are ways of “inheriting” behavior at runtime through composition and delegation. Master: Please, go on... Student: When I inherit behavior by subclassing, that behavior is set statically at compile time. In addition, all subclasses must inherit the same behavior. If however, I can extend an object’s behavior through composition, then I can do this dynamically at runtime. Master: Very good, Grasshopper, you are beginning to see the power of composition. Student: Yes, it is possible for me to add multiple new responsibilities to objects through this technique, including responsibilities that were not even thought of by the designer of the superclass. And, I don’t have to touch their code! Master: What have you learned about the effect of composition on maintaining your code? Student: Well, that is what I was getting at. By dynamically composing objects, I can add new functionality by writing new code rather than altering existing code. Because I’m not changing existing code, the chances of introducing bugs or causing unintended side effects in pre-existing code are much reduced. Master: Very good. Enough for today, Grasshopper. I would like for you to go and meditate further on this topic... Remember, code should be closed (to change) like the lotus flower in the evening, yet open (to extension) like the lotus flower in the morning.
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the open-closed principle
The Open-Closed Principle Grasshopper is on to one of the most important design principles:
Design Principle Classes should be open for extension, but closed for modification.
Come on in; we’re open. Feel free to extend our classes with any new behavior you like. If your needs or requirements change (and we know they will), just go ahead and make your own extensions. Sorry, we’re closed. That’s right, we spent a lot of time getting this code correct and bug free, so we can’t let you alter the existing code. It must remain closed to modification. If you don’t like it, you can speak to the manager.
Our goal is to allow classes to be easily extended to incorporate new behavior without modifying existing code. What do we get if we accomplish this? Designs that are resilient to change and flexible enough to take on new functionality to meet changing requirements.
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there are no
Dumb Questions
Q:
Open for extension and closed for modification? That sounds very contradictory. How can a design be both?
A:
That’s a very good question. It certainly sounds contradictory at first. After all, the less modifiable something is, the harder it is to extend, right? As it turns out, though, there are some clever OO techniques for allowing systems to be extended, even if we can’t change the underlying code. Think about the Observer Pattern (in Chapter 2)... by adding new Observers, we can extend the Subject at any time, without adding code to the Subject. You’ll see quite a few more ways of extending behavior with other OO design techniques.
Q:
Okay, I understand Observable, but how do I generally design something to be extensible, yet closed for modification?
A:
Usually, you can’t. Making OO design flexible and open to extension without the modification of existing code takes time and effort. In general, we don’t have the luxury of tying down every part of our designs (and it would probably be wastefu). Following the Open-Closed Principle usually introduces new levels of abstraction, which adds complexity to our code. You want to concentrate on those areas that are most likely to change in your designs and apply the principles there.
Q:
How do I know which areas of change are more important?
A:
That is partly a matter of experience in designing OO systems and also a matter of the knowing the domain you are working in. Looking at other examples will help you learn to identify areas of change in your own designs.
A:
While it may seem like a contradiction, there are techniques for allowing code to be extended without direct modification.
Q:
Be careful when choosing the areas of code that need to be extended; applying the Open-Closed Principle EVERYWHERE is wasteful, unnecessary, and can lead to complex, hard to understand code.
Many of the patterns give us time tested designs that protect your code from being modified by supplying a means of extension. In this chapter you’ll see a good example of using the Decorator pattern to follow the OpenClosed principle.
How can I make every part of my design follow the Open-Closed Principle?
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meet the decorator pattern
Meet the Decorator Pattern
Okay, enough of the “Object Oriented Design Club.” We have real problems here! Remember us? Starbuzz Coffee? Do you think you could use some of those design principles to actually help us?
Okay, we’ve seen that representing our beverage plus condiment pricing scheme with inheritance has not worked out very well – we get class explosions, rigid designs, or we add functionality to the base class that isn’t appropriate for some of the subclasses. So, here’s what we’ll do instead: we’ll start with a beverage and “decorate” it with the condiments at runtime. For example, if the customer wants a Dark Roast with Mocha and Whip, then we’ll:
1
Take a DarkRoast object
2
Decorate it with a Mocha object
3
Decorate it with a Whip object
4
Call the cost() method and rely on delegation to add on the condiment costs
Okay, but how do you “decorate” an object, and how does delegation come into this? A hint: think of decorator objects as “wrappers.” Let’s see how this works...
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Constructing a drink order with Decorators 1
We start with our DarkRoast object.
cost()
DarkRoast
2
t DarkRoaasnd has t a h t r e b Remem from Beverage mputes inherits method that co a cost() of the drink. the cost
The customer wants Mocha, so we create a Mocha object and wrap it around the DarkRoast.
or. Its ject is a decorisatdecorating, The Mocha obth object it type mirrors Beeverage. (By “mirror”, in this case, a the same type..) we mean it is
cost()
cost()
DarkRoast
Mocha
3
oo, st() method tn treat co a s a h a ch o e ca So, M olymorphism w and through p wrapped in Mocha as any Beveragetoo (because Mocha is a a Beverage, Beverage). subtype of
The customer also wants Whip, so we create a Whip decorator and wrap Mocha with it.
cost()
cost()
Whip
cost()
DarkRoast
Mocha
Whip is a decorator, so it also mirrors DarkRoast’s type and includes a cost() method.
So, a DarkRoast wrapped in Mocha and Whip is still a Beverage and we can do anything with it we can do with a DarkRoast, including call its cost() method. you are here 4
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decorator characteristics
4
Now it’s time to compute the cost for the customer. We do this by calling cost() on the outermost decorator, Whip, and Whip is going to delegate computing the cost to the objects it decorates. Once it gets a cost, it will add on the cost of the Whip.
in (You’ll see how ) s. ge a few pa
Mocha. 2 Whip calls cost() on t() on the 1 First, we call cos , Whip. tor ora dec st mo out
$1.29
.10
3
cost()
.20
cost()
Whip 5
Whip adds its total, 10 cents, to the result from Mocha, and returns the final result—$1.29.
5
Mocha calls cost() on DarkRoast.
cost()
t .99 D ar k Ro as
Mocha
4
Dar kRoast returns its cost, 99 cents.
Mocha adds its cost, 20 cents, to the result from Dar kRoast, and returns the new total, $1.19.
Okay, here’s what we know so far... ß Decorators have the same supertype as the objects they decorate. ß You can use one or more decorators to wrap an object. ß Given that the decorator has the same supertype as the object it decorates, we can pass around a decorated object in place of the original (wrapped) object.
ß The decorator adds its own behavior either before and/or after delegating to the object it decorates to do the rest of the job.
ß Objects can be decorated at any time, so we can decorate objects dynamically at runtime with as many decorators as we like.
Now let’s see how this all really works by looking at the Decorator Pattern definition and writing some code. 90
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t Key Poin
!
the decorator pattern
The Decorator Pattern defined Let’s first take a look at the Decorator Pattern description: The Decorator Pattern attaches additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.
While that describes the role of the Decorator Pattern, it doesn’t give us a lot of insight into how we’d apply the pattern to our own implementation. Let’s take a look at the class diagram, which is a little more revealing (on the next page we’ll look at the same structure applied to the beverage problem).
Each component can be used on its own, or wrapped by a decorator.
Component
component
methodA() methodB()
The ConcreteComponent is the object we’re going to dynamically add new behavior to. It extends Component.
// other methods
Decorator
ConcreteComponent methodA()
methodA()
methodB()
methodB()
// other methods
// other methods
ConcereteDecoratorA Component wrappedObj
s an The ConcreteDecoratorehathing th r fo ble instance varia t it decorates (the Componen s). ap wr r the Decorato
Each decorator HAS-A (wraps) a component, which means the decorator has an instance variable that holds a reference to a component.
ent the Decorators implem abstract same interfacemorponent they class as the co corate. are going to de ConcereteDecoratorB Component wrappedObj Object newState
methodA() methodB()
methodA()
newBehavior() // other methods
methodB() // other methods
e Decorators can extendt.th en on mp state of the co
Decorators can add new methods; however, new behavior is typically added by doing computation before or after an existing method in the component. you are here 4
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decorating beverages
Decorating our Beverages Okay, let’s work our Starbuzz beverages into this framework...
r Beverage acts asneou class. nt po m abstract co
component
Beverage description
getDescription() cost() // other useful methods
CondimentDecorator
DarkRoast
HouseBlend cost()
cost()
getDescription()
Decaf
Espresso cost()
cost()
e concretper r u o f e e Th nents, on compo e type. coffe
Milk
Whip
Soy
Mocha
Beverage beverage
Beverage beverage
Beverage beverage
Beverage beverage
cost()
cost()
cost()
cost()
getDescription()
getDescription()
getDescription()
getDescription()
And here are our condiment decorators; notice they need to implement not only cost() but also getDescription(). We’ll see why in a moment...
A
brain power
Before going further, think about how you’d implement the cost() method of the coffees and the condiments. Also think about how you’d implement the getDescription() method of the condiments.
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Cubicle Conversation Some confusion over Inheritance versus Composition
ry
Ma
Okay, I’m a little confused...I thought we weren’t going to use inheritance in this pattern, but rather we were going to rely on composition instead.
Sue: What do you mean? Mary: Look at the class diagram. The CondimentDecorator is extending the Beverage class. That’s inheritance, right? Sue: True. I think the point is that it’s vital that the decorators have the same type as the objects they are going to decorate. So here we’re using inheritance to achieve the type matching, but we aren’t using inheritance to get behavior. Mary: Okay, I can see how decorators need the same “interface” as the components they wrap because they need to stand in place of the component. But where does the behavior come in? Sue: When we compose a decorator with a component, we are adding new behavior. We are acquiring new behavior not by inheriting it from a superclass, but by composing objects together. Mary: Okay, so we’re subclassing the abstract class Beverage in order to have the correct type, not to inherit its behavior. The behavior comes in through the composition of decorators with the base components as well as other decorators. Sue: That’s right. Mary: Ooooh, I see. And because we are using object composition, we get a whole lot more flexibility about how to mix and match condiments and beverages. Very smooth. Sue: Yes, if we rely on inheritance, then our behavior can only be determined statically at compile time. In other words, we get only whatever behavior the superclass gives us or that we override. With composition, we can mix and match decorators any way we like... at runtime. Mary: And as I understand it, we can implement new decorators at any time to add new behavior. If we relied on inheritance, we’d have to go in and change existing code any time we wanted new behavior. Sue: Exactly. Mary: I just have one more question. If all we need to inherit is the type of the component, how come we didn’t use an interface instead of an abstract class for the Beverage class? Sue: Well, remember, when we got this code, Starbuzz already had an abstract Beverage class. Traditionally the Decorator Pattern does specify an abstract component, but in Java, obviously, we could use an interface. But we always try to avoid altering existing code, so don’t “fix” it if the abstract class will work just fine. you are here 4
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decorator training
New barista training
Okay, I need for you to make me a double mocha, soy latte with whip.
Make a picture for what happens when the order is for a “double mocha soy lotte with whip” beverage. Use the menu to get the correct prices, and draw your picture using the same format we used earlier (from a few pages back): Mocha. 2 Whip calls cost() on
3
) on the 1 First, we call cost( outmost decorator, Whip.
$1.29
.10
cost()
.20
cost()
Whip 5
Whip adds its total, 10 cents, to the result from Mocha, and returns the final result—$1.29.
5
Mocha calls cost() on DarkRoast.
was for This picturoeast mocha a “dark r rage. whip” beve
cost()
t .99 D ar k Ro as
Mocha
4
DarkRoast returns its cost, 99 cents.
Mocha adds its cost, 20 cents, to the result from DarkRoast, and returns the new total, $1.19.
Sharpen your pencil
Draw your picture here.
Starbuzz Coffee
Coffees House Blend .89 Dark Roast .99 Decaf 1.05 Espresso 1.99 Condiments Steamed Milk .10 Mocha .20 Soy .15 Whip .10
bu tar zz
u tarb zz
ffee S Co
fe Cof e S
le “doub ke a whip” a m n h ca oy, : you te wit nd, S ! HINTha soy lat HouseBle and Whip moc ombining Mocha by c shots of two
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Writing the Starbuzz code It’s time to whip this design into some real code. Let’s start with the Beverage class, which doesn’t need to change from Starbuzz’s original design. Let’s take a look:
public abstract class Beverage { String description = “Unknown Beverage”; public String getDescription() { return description; } public abstract double cost(); }
abstract Beverage is an two methods class with the n() and cost(). getDescriptio
getDescription is already implemented for us, but we need to implement cost() in the subclasses.
Beverage is simple enough. Let’s implement the abstract class for the Condiments (Decorator) as well:
to be First, we needle with a Beverage, interchangeab the Beverage class. so we extend public abstract class CondimentDecorator extends Beverage { public abstract String getDescription(); }
We’re also going to require that the condiment decorators all reimplement the getDescription() method. Again, we’ll see why in a sec...
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implementing the beverages
Coding beverages Now that we’ve got our base classes out of the way, let’s implement some beverages. We’ll start with Espresso. Remember, we need to set a description for the specific beverage and also implement the cost() method.
public class Espresso extends Beverage { public Espresso() { description = “Espresso”; } public double cost() { return 1.99; } }
public double cost() { return .89; }
Okay, here’s another Beverage. All we do is set the appropriate description, “House Blend Coffee,” and then return the correct cost: 89¢. You can create the other two Beverage classses (DarkRoast and Decaf) in exactly the same way.
96
we To take care of the description,the for or uct str con set this in the instance class. Remember the description ge. variable is inherited from Bevera
’t spresso. We djuonst E an of st co e to compute th this class, we Finally, we needabout adding in condiments in.99. need to worry the price of an Espresso: $1 need to return
public class HouseBlend extends Beverage { public HouseBlend() { description = “House Blend Coffee”; }
}
d the Beverage First we exthiens is a beverage. class, since t
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Coffee Starbuzz s Coffee Blend House oast R Dark Decaf so Espres
.89 .99 1.05 1.99
ents Condim d Milk Steame Mocha Soy Whip
.10 .20 .15 .10
the decorator pattern
Coding condiments If you look back at the Decorator Pattern class diagram, you’ll see we’ve now written our abstract component (Beverage), we have our concrete components (HouseBlend), and we have our abstract decorator (CondimentDecorator). Now it’s time to implement the concrete decorators. Here’s Mocha:
tor tDecora n e im d n o Mocha is a decorator, so we e Mocha with at ti an mber, Cverage. st e in m to e g in R We’re go extend CondimentDecorator. Be Beverage using: extends a reference to a e variable to hold th (1) An instancewrapping. public class Mocha extends CondimentDecorator { beverage we are Beverage beverage; t this instance (2) A way to seject we are wrapping. public Mocha(Beverage beverage) { variable to theinob pass the beverage this.beverage = beverage; ere, we’re go g tothe decorator’s H } we’re wrapping to constructor. public String getDescription() { return beverage.getDescription() + “, Mocha”; } public double cost() { return .20 + beverage.cost(); } }
beverage ute the cost of oullr to mp co to ed e ne we w No delegate the ca mpth we t, rs Fi . ha e the oc ut M th co wi ng, so that it can to the result. ti ra co de ’re we ct je ob e cost of Mocha cost; then, we add th
We want our description to not only include the beverage - say “Dark Roast” - but also to include each item decorating the beverage, for instance, “Dark Roast, Mocha”. So we first delegate to the object we are decorating to get its description, then append “, Mocha” to that description.
On the next page we’ll actually instantiate the beverage and wrap it with all its condiments (decorators), but first... Sharpen your pencil
Write and compile the code for the other Soy and Whip condiments. You’ll need them to finish and test the application.
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testing the beverages
Serving some coffees Congratulations. It’s time to sit back, order a few coffees and marvel at the flexible design you created with the Decorator Pattern.
Here’s some test code to make orders: public class StarbuzzCoffee { public static void main(String args[]) { Beverage beverage = new Espresso(); System.out.println(beverage.getDescription() + “ $” + beverage.cost());
s condimentt. o n , o s s e nd cos an espr Order upt its description a and prin
oast object. Make a DarkR Beverage beverage2 = new DarkRoast(); Wrap it with a Mocha. beverage2 = new Mocha(beverage2); Wrap it in a second Mocha. beverage2 = new Mocha(beverage2); beverage2 = new Whip(beverage2); Wrap it in a Whip. System.out.println(beverage2.getDescription() + “ $” + beverage2.cost()); Beverage beverage3 = new HouseBlend(); beverage3 = new Soy(beverage3); beverage3 = new Mocha(beverage3); beverage3 = new Whip(beverage3); System.out.println(beverage3.getDescription() + “ $” + beverage3.cost());
Finally, give us a HouseBlend with Soy, Mocha, and Whip.
} }
Now, let’s get those orders in:
We’re going to see a much better way of creating decorated objects when we cover the Factory and Builder Design Patterns.
File Edit Window Help CloudsInMyCoffee
% java StarbuzzCoffee Espresso $1.99 Dark Roast Coffee, Mocha, Mocha, Whip $1.49 File Edit Window Help CloudsInMyCoffee House Blend Coffee, Soy, Mocha, Whip $1.34 %
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there are no
Dumb Questions
Q:
I’m a little worried about code that might test for a specfic concrete component – say, HouseBlend – and do something, like issue a discount. Once I’ve wrapped the HouseBlend with decorators, this isn’t going to work anymore.
A:
That is exactly right. If you have code that relies on the concrete component’s type, decorators will break that code. As long as you only write code against the abstract component type, the use of decorators will remain transparent to your code. However, once you start writing code against concrete components, you’ll want to rethink your application design and your use of decorators.
Q:
Wouldn’t it be easy for some client of a beverage to end up with a decorator that isn’t the outermost decorator? Like if I had a DarkRoast with Mocha, Soy, and Whip, it would be easy to write code that somehow ended up with a reference to Soy instead of Whip, which means it would not including Whip in the order.
A:
You could certainly argue that you have to manage more objects with the Decorator Pattern and so there is an increased chance that coding errors will introduce the kinds of problems you suggest. However, decorators are typically created by using other patterns like Factory and Builder. Once we’ve covered these patterns, you’ll see that the creation of the concrete component with its decorator is “well encapsulated” and doesn’t lead to these kinds of problems.
Q:
Can decorators know about the other decorations in the chain? Say, I wanted my getDecription() method to print “Whip, Double Mocha” instead of “Mocha, Whip, Mocha”? That would require that my outermost decorator know all the decorators it is wrapping.
A:
Decorators are meant to add behavior to the object they wrap. When you need to peek at multiple layers into the decorator chain, you are starting to push the decorator beyond its true intent. Nevertheless, such things are possible. Imagine a CondimentPrettyPrint decorator that parses the final decription and can print “Mocha, Whip, Mocha” as “Whip, Double Mocha.” Note that getDecription() could return an ArrayList of descriptions to make this easier.
Sharpen your pencil Our friends at Starbuzz have introduced sizes to their menu. You can now order a coffee in tall, grande, and venti sizes (translation: small, medium, and large). Starbuzz saw this as an intrinsic part of the coffee class, so they’ve added two methods to the Beverage class: setSize() and getSize(). They’d also like for the condiments to be charged according to size, so for instance, Soy costs 10¢, 15¢ and 20¢ respectively for tall, grande, and venti coffees. How would you alter the decorator classes to handle this change in requirements?
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decorators in java i/o
Real World Decorators: Java I/O The large number of classes in the java.io package is... overwhelming. Don’t feel alone if you said “whoa” the first (and second and third) time you looked at this API. But now that you know the Decorator Pattern, the I/O classes should make more sense since the java.io package is largely based on Decorator. Here’s a typical set of objects that use decorators to add functionality to reading data from a file:
A text file for reading.
ered
e InputStr
a
ff
m
ne Nu mberInputStrea
LineNumberInputStream is also a concrete decorator. It adds the ability to count the line numbers as it reads data.
m
Li
Bu
FileInputStream
BufferedInputStream is a concrete decorator. BufferedInputStream adds behavior in two ways: it buffers input to improve performance, and also augments the interface with a new method readLine() for reading character-based input, a line at a time.
BufferedInputStream and LineNumberInputStream both extend FilterInputStream, which acts as the abstract decorator class.
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hat’s component tary e h t is m a e r FileInputStr ted. The Java I/O lib g a in r d o c lu e c nts, in being d ral compone BufferInputStream, e v se s e li p p su others. eam, String FileInputStr putStream and a fewent from ByteArrayIn give us a base compon All of thesead bytes. which to re
the decorator pattern
Decorating the java.io classes ent. ract compon st b a r u o ’s Here
FilterInputStream is an abstract decorator.
InputStream
FileInputStream
StringBufferInputStream
PushbackInputStream
These InputStreams act as the concrete components that we will wrap with decorators. There are a few more we didn’t show, like ObjectInputStream.
FilterInputStream
ByteArrayInputStream
BufferedInputStream
DataInputStream
LineNumberInputStream
crete decorators.
And finally, here are all our con
You can see that this isn’t so different from the Starbuzz design. You should now be in a good position to look over the java.io API docs and compose decorators on the various input streams. You’ll see that the output streams have the same design. And you’ve probably already found that the Reader/Writer streams (for character-based data) closely mirror the design of the streams classes (with a few differences and inconsistencies, but close enough to figure out what’s going on). Java I/O also points out one of the downsides of the Decorator Pattern: designs using this pattern often result in a large number of small classes that can be overwhelming to a developer trying to use the Decorator-based API. But now that you know how Decorator works, you can keep things in perspective and when you’re using someone else’s Decorator-heavy API, you can work through how their classes are organized so that you can easily use wrapping to get the behavior you’re after.
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write your own i/o decorator
Writing your own Java I/O Decorator Okay, you know the Decorator Pattern, you’ve seen the I/O class diagram. You should be ready to write your own input decorator. How about this: write a decorator that converts all uppercase characters to lowercase in the input stream. In other words, if we read in “I know the Decorator Pattern therefore I RULE!” then your decorator converts this to “i know the decorator pattern therefore i rule!”
t to import e g r o f ’t n o D t shown) java.io... (no
No problem. I just have to extend the FilterInputStream class and override the read() methods.
First, extend the FilterInputStream, the abstract decorator for all InputStreams.
public class LowerCaseInputStream extends FilterInputStream { public LowerCaseInputStream(InputStream in) { super(in); } public int read() throws IOException { int c = super.read(); return (c == -1 ? c : Character.toLowerCase((char)c)); }
}
public int read(byte[] b, int offset, int len) throws IOException { int result = super.read(b, offset, len); for (int i = offset; i < offset+result; i++) { b[i] = (byte)Character.toLowerCase((char)b[i]); Now we need to implement two } read methods. They take a return result; byte (or an array of bytes) } convert each byte (that
and represents a character) to lowercase if it’s an uppercase character.
REMEMBER: we don’t provide import and package statements in the code listings. Get the complete source code from the wickedlysmart web site. You’ll find the URL on page xxxiii in the Intro. 102
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the decorator pattern
Test out your new Java I/O Decorator Write some quick code to test the I/O decorator: public class InputTest { public static void main(String[] args) throws IOException { int c; try { m InputStream in = ileInputStrea new LowerCaseInputStream( Set up the tFe it, first with new BufferedInputStream( and decoradInputStream new FileInputStream(“test.txt”))); Buffere while((c = in.read()) >= 0) { System.out.print((char)c); } in.close(); } catch (IOException e) { e.printStackTrace(); } } }
a brand new and then ouInr putStream filter. LowerCase
I know the Decorator Pattern therefore I RULE!
Just use the stream to read characters until the end of file and print as we go.
test.txt file
You need tfoile. make this
Give it a spin: File Edit Window Help DecoratorsRule
% java InputTest i know the decorator pattern therefore i rule! %
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103
decorator interview
Patterns Exposed This week’s interview:
Confessions of a Decorator HeadFirst: Welcome Decorator Pattern. We’ve heard that you’ve been a bit down on yourself lately? Decorator: Yes, I know the world sees me as the glamorous design pattern, but you know, I’ve got my share of problems just like everyone. HeadFirst: Can you perhaps share some of your troubles with us? Decorator: Sure. Well, you know I’ve got the power to add flexibility to designs, that much is for sure, but I also have a dark side. You see, I can sometimes add a lot of small classes to a design and this occasionally results in a design that’s less than straightforward for others to understand. HeadFirst: Can you give us an example? Decorator: Take the Java I/O libraries. These are notoriously difficult for people to understand at first. But if they just saw the classes as a set of wrappers around an InputStream, life would be much easier. HeadFirst: That doesn’t sound so bad. You’re still a great pattern, and improving this is just a matter of public education, right? Decorator: There’s more, I’m afraid. I’ve got typing problems: you see, people sometimes take a piece of client code that relies on specific types and introduce decorators without thinking through everything. Now, one great thing about me is that you can usually insert decorators transparently and the client never has to know it’s dealing with a decorator. But like I said, some code is dependent on specific types and when you start introducing decorators, boom! Bad things happen. HeadFirst: Well, I think everyone understands that you have to be careful when inserting decorators, I don’t think this is a reason to be too down on yourself. Decorator: I know, I try not to be. I also have the problem that introducing decorators can increase the complexity of the code needed to instantiate the component. Once you’ve got decorators, you’ve got to not only instantiate the component, but also wrap it with who knows how many decorators. HeadFirst: I’ll be interviewing the Factory and Builder patterns next week – I hear they can be very helpful with this? Decorator: That’s true; I should talk to those guys more often. HeadFirst: Well, we all think you’re a great pattern for creating flexible designs and staying true to the Open-Closed Principle, so keep your chin up and think positively! Decorator: I’ll do my best, thank you. 104
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the decorator pattern
Tools for your Design Toolbox
BULLET POINTS
You’ve got another chapter under your belt and a new principle and pattern in the toolbox.
ß Inheritance is one form of extension, but not necessarily the best way to achieve flexibility in our designs.
ß In our designs we should allow behavior to be extended without the need to modify existing code.
OO Basincs Abstractio tion s OO Principle Encapsulaphism Polymor hat varies. w e t la su p a Enc nchee. ritance eritaIn h in r e v o n ositio Favor comp not interfaces, Program to s. ion implementat gns coupled desi ly se o lo r o Strive f eract. ts that int c je b o n e e w bet for
ld be open r u o h s s e s s la o C ut closed f extension b n. modificatio
ß Composition and delegation can often be used to add new behaviors at runtime.
ß The Decorator Pattern provides an alternative to subclassing for extending behavior.
ß The Decorator Pattern involves a set of decorator classes that are used to wrap concrete components.
ß We now have the Open-Closed g Principle to guide us. We’re goin to strive to design our system so that the closed parts are . isolated from our new extensions
Decorator classes mirror the type of the components they decorate. (In fact, they are the same type as the components they decorate, either through inheritance or interface implementation.)
ß Decorators change the behavior
OO Patterr-ndsefineysofa aolgneor-itthom-s,tmhaanty
bys-erdvefeinyesbaetfwameilenkeosbjethcetms soddaitllioitnsal O g e t a r St depenedaecnhcone, andrm-aanAgtets ascthaotareit, hm o ch lg pddaytneadmically. encapsuwlahteensDoenc.e oSortbrajeattcetgy slettsoietahdne aaonbdjecutit able ilritme ienclioetnifts thaat fulesexib. le a interchdanegpeernedseptnolytnsib r tending nden f o s provide vary indaeupteoDmeactoicralltyor o subclassing for ex t alternative y. t functionali designs n for creatingOr was it er t t pa st ir f r . And here’s ou the Open-Closed Principle ern we’ve that satisfy st? Is there another patt really the fir lows this principle as well? used that fol www.it-ebooks.info
of their components by adding new functionality before and/or after (or even in place of) method calls to the component.
ß You can wrap a component with any number of decorators.
ß Decorators are typically transparent to the client of the component; that is, unless the client is relying on the component’s concrete type.
ß Decorators can result in many small objects in our design, and overuse can be complex. you are here 4
105
exercise solutions
Exercise solutions public class Beverage { // declare instance variables for milkCost, // soyCost, mochaCost, and whipCost, and // getters and setters for milk, soy, mocha // and whip.
public class DarkRoast extends Beverage { public DarkRoast() { description = “Most Excellent Dark Roast”; }
public float cost() { float condimentCost = 0.0; if (hasMilk()) { condimentCost += milkCost; } if (hasSoy()) { condimentCost += soyCost; } if (hasMocha()) { condimentCost += mochaCost; } if (hasWhip()) { condimentCost += whipCost; } return condimentCost;
public float cost() { return 1.99 + super.cost();
}
}
} }
New barista training
“double mocha soy lotte with whip” on Mocha 2 Whip calls cost() another Mocha. 3 Mocha calls cost() on the Mocha calls cost() on Soy. First, we call cost() on 4 Next, 1 outmost decorator, Whip. Soy calls 5 Last topping! cost() on HouseBlend.
6
offee
tarbu
zz C
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.10
cost()
cost() cost()
.20
S
W
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.20
M
hip
Mo
cha
oc
ha
cost()
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y
11 Finally, the result returns to
Whip’s cost(), which adds .10 and we have a final cost of $1.54.
106
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cost()
.89 nd HouseBle
7
8
9
HouseBlend’s cost() method returns .89 cents and pops off the stack. Soy’s cost() method adds .15 and returns the result, and pops off the stack.
The second Mocha’s cost() method adds .20 and returns the result, and pops off the stack.
method The first Mocha’s cost() result, adds .20 and returns the and pops off the stack.
the decorator pattern
Exercise solutions Our friends at Starbuzz have introduced sizes to their menu. You can now order a coffee in tall, grande, and venti sizes (for us normal folk: small, medium, and large). Starbuzz saw this as an intrinsic part of the coffee class, so they’ve added two methods to the Beverage class: setSize() and getSize(). They’d also like for the condiments to be charged according to size, so for instance, Soy costs 10¢, 15¢, and 20¢ respectively for tall, grande, and venti coffees. How would you alter the decorator classes to handle this change in requirements?
public class Soy extends CondimentDecorator { Beverage beverage; public Soy(Beverage beverage) { this.beverage = beverage; } public getSize() { return beverage.getSize(); }
propagate the Now we need thoo d to the wrapped getSize() mete should also move this beverage. W he abstract class since method to t l condiment decorators. it’s used in al
public String getDescription() { return beverage.getDescription() + “, Soy”; } public double cost() { double cost = beverage.cost(); if (getSize() == Beverage.TALL) { cost += .10; } else if (getSize() == Beverage.GRANDE) { cost += .15; } else if (getSize() == Beverage.VENTI) { cost += .20; } return cost; }
Here we get the size (which propagates all the way to the concrete beverage) and then add the appropriate cost.
}
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107
Chapter 4. Baking with OO Goodness
Table of Contents Chapter 4. Baking with OO Goodness.......................................................... 1 Section 4.1. Brain Power................................................................................................................................................................. 3 Section 4.2. Identifying the aspects that vary................................................................................................................................. 4 Section 4.3. But the pressure is on to add more pizza types.......................................................................................................... 5 Section 4.4. Encapsulating object creation..................................................................................................................................... 6 Section 4.5. Building a simple pizza factory................................................................................................................................... 7 Section 4.6. There are no Dumb Questions.................................................................................................................................... 7 Section 4.7. Reworking the PizzaStore class.................................................................................................................................. 8 Section 4.8. The Simple Factory defined........................................................................................................................................ 9 Section 4.9. Franchising the pizza store....................................................................................................................................... 10 Section 4.10. A framework for the pizza store.............................................................................................................................. 12 Section 4.11. Allowing the subclasses to decide............................................................................................................................ 13 Section 4.12. Let's make a PizzaStore............................................................................................................................................ 15 Section 4.13. Declaring a factory method...................................................................................................................................... 17 Section 4.14. Let's see how it works: ordering pizzas with the pizza factory method.................................................................. 18 Section 4.15. Let's check out how these pizzas are really made to order... Behind the Scenes.................................................... 19 Section 4.16. We're just missing one thing: PIZZA!..................................................................................................................... 20 Section 4.17. Now we just need some concrete subclasses... how about defining New York and Chicago style cheese pizzas?..... 21 Section 4.18. It's finally time to meet the Factory Method Pattern............................................................................................. 23 Section 4.19. Another perspective: parallel class hierarchies...................................................................................................... 24 Section 4.20. Design Puzzle.......................................................................................................................................................... 25 Section 4.21. Factory Method Pattern defined............................................................................................................................. 26 Section 4.22. There are no Dumb Questions................................................................................................................................ 27 Section 4.23. A very dependent PizzaStore.................................................................................................................................. 29 Section 4.24. Looking at object dependencies............................................................................................................................. 30 Section 4.25. The Dependency Inversion Principle...................................................................................................................... 31 Section 4.26. Applying the Principle............................................................................................................................................ 32 Section 4.27. Inverting your thinking........................................................................................................................................... 34 Section 4.28. A few guidelines to help you follow the Principle.................................................................................................. 35 Section 4.29. Meanwhile, back at the PizzaStore......................................................................................................................... 36 Section 4.30. Families of ingredients........................................................................................................................................... 37 Section 4.31. Building the ingredient factories............................................................................................................................ 38 Section 4.32. Building the New York ingredient factory.............................................................................................................. 39 Section 4.33. Sharpen your pencil................................................................................................................................................ 40 Section 4.34. Reworking the pizzas............................................................................................................................................... 41 Section 4.35. Reworking the pizzas, continued............................................................................................................................ 42 Section 4.36. Code Up Close......................................................................................................................................................... 43 Section 4.37. Revisiting our pizza stores...................................................................................................................................... 44 Section 4.38. What have we done?............................................................................................................................................... 45 Section 4.39. More pizza for Ethan and Joel................................................................................................................................ 46 Section 4.40. Abstract Factory Pattern defined........................................................................................................................... 48 Section 4.41. Patterns Exposed..................................................................................................................................................... 50 Section 4.42. Factory Method and Abstract Factory compared................................................................................................... 52 Section 4.43. Tools for your Design Toolbox................................................................................................................................ 54 Section 4.44. Exercise solutions................................................................................................................................................... 56 Section 4.45. Sharpen your pencil................................................................................................................................................ 56 Section 4.46. Design Puzzle Solution............................................................................................................................................ 57 Section 4.47. A very dependent PizzaStore.................................................................................................................................. 58 Section 4.48. Sharpen your pencil................................................................................................................................................ 58 Section 4.49. Sharpen your pencil................................................................................................................................................ 59 Section 4.50. Puzzle Solution....................................................................................................................................................... 60
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 17
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 18
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 20
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 21
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 22
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 23
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 24
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 27
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID:
[email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 4. Baking with OO Goodness Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 5. One of a Kind Objects
Table of Contents Chapter 5. One of a Kind Objects................................................................. 1 Section 5.1. The Little Singleton: A small Socratic exercise in the style of The Little Lisper........................................................ 3 Section 5.2. Dissecting the classic Singleton Pattern implementation.......................................................................................... 5 Section 5.3. Patterns Exposed......................................................................................................................................................... 6 Section 5.4. The Chocolate Factory................................................................................................................................................. 7 Section 5.5. Sharpen your pencil.................................................................................................................................................... 8 Section 5.6. Singleton Pattern defined........................................................................................................................................... 9 Section 5.7. Hershey, PA: Houston, we have a problem............................................................................................................... 10 Section 5.8. BE the JVM................................................................................................................................................................ 11 Section 5.9. Dealing with multithreading..................................................................................................................................... 12 Section 5.10. Can we improve multithreading?............................................................................................................................ 13 Section 5.11. Meanwhile, back at the Chocolate Factory.............................................................................................................. 15 Section 5.12. Congratulations!....................................................................................................................................................... 15 Section 5.13. there are no Dumb Questions.................................................................................................................................. 16 Section 5.14. Tools for your Design Toolbox................................................................................................................................ 18 Section 5.15. Exercise solutions.................................................................................................................................................... 20 Section 5.16. Exercise Solutions.................................................................................................................................................... 21 Section 5.17. Exercise solutions.................................................................................................................................................... 22
Chapter 5. One of a Kind Objects Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 5. One of a Kind Objects
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Chapter 5. One of a Kind Objects
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Chapter 5. One of a Kind Objects Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 5. One of a Kind Objects Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 5. One of a Kind Objects Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 5. One of a Kind Objects Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 5. One of a Kind Objects Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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there are no Dumb Questions
Q:
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&OR SUCH A SIMPLE PATTERN CONSISTING OF ONLY ONE CLASS 3INGLETONS SURE SEEM TO HAVE SOME PROBLEMS
#ANT ) JUST CREATE A CLASS IN WHICH ALL METHODS AND VARIABLES ARE DElNED AS STATIC 7OULDNT THAT BE THE SAME AS A 3INGLETON
7ELL WE WARNED YOU UP FRONT "UT DONT LET THE PROBLEMS DISCOURAGE YOU WHILE IMPLEMENTING 3INGLETONS CORRECTLY CAN BE TRICKY AFTER READING THIS CHAPTER YOU ARE NOW WELL INFORMED ON THE TECHNIQUES FOR CREATING 3INGLETONS AND SHOULD USE THEM WHEREVER YOU NEED TO CONTROL THE NUMBER OF INSTANCES YOU ARE CREATING
9ES IF YOUR CLASS IS SELF CONTAINED AND DOESNT DEPEND ON COMPLEX INITIALIZATION (OWEVER BECAUSE OF THE WAY STATIC INITIALIZATIONS ARE HANDLED IN *AVA THIS CAN GET VERY MESSY ESPECIALLY IF MULTIPLE CLASSES ARE INVOLVED /FTEN THIS SCENARIO CAN RESULT IN SUBTLE HARD TO FIND BUGS INVOLVING ORDER OF INITIALIZATION 5NLESS THERE IS A COMPELLING NEED TO IMPLEMENT YOUR hSINGLETONv THIS WAY IT IS FAR BETTER TO STAY IN THE OBJECT WORLD
7HAT ABOUT CLASS LOADERS ) HEARD THERE IS A CHANCE THAT TWO CLASS LOADERS COULD EACH END UP WITH THEIR OWN INSTANCE OF 3INGLETON
9ES THAT IS TRUE AS EACH CLASS LOADER DEFINES A NAMESPACE )F YOU HAVE TWO OR MORE CLASSLOADERS YOU CAN LOAD THE SAME CLASS MULTIPLE TIMES ONCE IN EACH CLASSLOADER .OW IF THAT CLASS HAPPENS TO BE A 3INGLETON THEN SINCE WE HAVE MORE THAN ONE VERSION OF THE CLASS WE ALSO HAVE MORE THAN ONE INSTANCE OF THE 3INGLETON 3O IF YOU ARE USING MULTIPLE CLASSLOADERS AND 3INGLETONS BE CAREFUL /NE WAY AROUND THIS PROBLEM IS TO SPECIFY THE CLASSLOADER YOURSELF
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Q:
)VE ALWAYS BEEN TAUGHT THAT A CLASS SHOULD DO ONE THING AND ONE THING ONLY &OR A CLASS TO DO TWO THINGS IS CONSIDERED BAD // DESIGN )SNT A 3INGLETON VIOLATING THIS
A:
9OU WOULD BE REFERRING TO THE h/NE #LASS /NE 2ESPONSIBILITYv PRINCIPLE AND YES YOU ARE CORRECT THE 3INGLETON IS NOT ONLY RESPONSIBLE FOR MANAGING ITS ONE INSTANCE AND PROVIDING GLOBAL ACCESS IT IS ALSO RE SPONSIBLE FOR WHATEVER ITS MAIN ROLE IS IN YOUR APPLICATION 3O CERTAINLY IT CAN BE ARGUED IT IS TAKING ON TWO RESPON SIBILITIES .EVERTHELESS IT ISNT HARD TO SEE THAT THERE IS UTILITY IN A CLASS MANAGING ITS OWN INSTANCE IT CERTAINLY MAKES THE OVERALL DESIGN SIMPLER )N ADDITION MANY DEVELOPERS ARE FAMILIAR WITH THE 3INGLETON PATTERN AS IT IS IN WIDE USE 4HAT SAID SOME DEVELOPERS DO FEEL THE NEED TO ABSTRACT OUT THE 3INGLETON FUNCTIONALITY
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) WANTED TO SUBCLASS MY 3INGLETON CODE BUT ) RAN INTO PROBLEMS )S IT OKAY TO SUBCLASS A 3INGLETON
/NE PROBLEM WITH SUBCLASSING 3INGLETON IS THAT THE CONSTRUCTOR IS PRIVATE 9OU CANT EXTEND A CLASS WITH A PRIVATE CONSTRUCTOR 3O THE FIRST THING YOULL HAVE TO DO IS CHANGE YOUR CONSTRUCTOR SO THAT ITS PUBLIC OR PROTECTED "UT THEN ITS NOT REALLY A 3INGLETON ANYMORE BECAUSE OTHER CLASSES CAN INSTANTIATE IT )F YOU DO CHANGE YOUR CONSTRUCTOR THERES ANOTHER ISSUE 4HE IMPLEMENTATION OF 3INGLETON IS BASED ON A STATIC VARIABLE SO IF YOU DO A STRAIGHTFORWARD SUBCLASS ALL OF YOUR DERIVED CLASSES WILL SHARE THE SAME INSTANCE VARIABLE 4HIS IS PROBABLY NOT WHAT YOU HAD IN MIND 3O FOR SUBCLASSING TO WORK IMPLEMENTING REGISTRY OF SORTS IS REQUIRED IN THE BASE CLASS
) STILL DONT TOTALLY UNDERSTAND WHY GLOBAL VARIABLES ARE WORSE THAN A 3INGLETON
)N *AVA GLOBAL VARIABLES ARE BASICALLY STATIC REFERENCES TO OBJECTS 4HERE ARE A COUPLE OF DISADVANTAGES TO USING GLOBAL VARIABLES IN THIS MANNER 7EVE ALREADY MENTIONED ONE THE ISSUE OF LAZY VERSUS EAGER INSTANTIATION "UT WE NEED TO KEEP IN MIND THE INTENT OF THE PATTERN TO ENSURE ONLY ONE INSTANCE OF A CLASS EXISTS AND TO PROVIDE GLOBAL ACCESS ! GLOBAL VARIABLE CAN PROVIDE THE LATTER BUT NOT THE FORMER 'LOBAL VARIABLES ALSO TEND TO ENCOURAGE DEVELOPERS TO POLLUTE THE NAMESPACE WITH LOTS OF GLOBAL REFERENCES TO SMALL OBJECTS 3INGLETONS DONT ENCOURAGE THIS IN THE SAME WAY BUT CAN BE ABUSED NONETHELESS
"EFORE IMPLEMENTING SUCH A SCHEME YOU SHOULD ASK YOURSELF WHAT YOU ARE REALLY GAINING FROM SUBCLASSING A 3INGLETON ,IKE MOST PATTERNS THE 3INGLETON IS NOT NECESSARILY MEANT TO BE A SOLUTION THAT CAN FIT INTO A LIBRARY )N ADDITION THE 3INGLETON CODE IS TRIVIAL TO ADD TO ANY EXISTING CLASS ,AST IF YOU ARE USING A LARGE NUMBER OF 3INGLETONS IN YOUR APPLICATION YOU SHOULD TAKE A HARD LOOK AT YOUR DESIGN 3INGLETONS ARE MEANT TO BE USED SPARINGLY
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Chapter 5. One of a Kind Objects Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 5. One of a Kind Objects Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Encapsulating Invocation
Table of Contents Chapter 6. Encapsulating Invocation........................................................... 1 Section 6.1. Free hardware! Let's check out the Remote Control.................................................................................................. 3 Section 6.2. Taking a look at the vendor classes............................................................................................................................ 4 Section 6.3. Cubicle Conversation.................................................................................................................................................. 5 Section 6.4. Meanwhile, back at the Diner..., or, A brief introduction to the Command Pattern................................................. 7 Section 6.5. Let's study the interaction in a little more detail....................................................................................................... 8 Section 6.6. The Objectville Diner roles and responsibilities........................................................................................................ 9 Section 6.7. From the Diner to the Command Pattern................................................................................................................. 11 Section 6.8. Our first command object......................................................................................................................................... 13 Section 6.9. Using the command object........................................................................................................................................ 14 Section 6.10. Creating a simple test to use the Remote Control................................................................................................... 14 Section 6.11. Sharpen your pencil.................................................................................................................................................. 15 Section 6.12. The Command Pattern defined............................................................................................................................... 16 Section 6.13. The Command Pattern defined: the class diagram................................................................................................. 17 Section 6.14. BRAIN POWER........................................................................................................................................................ 17 Section 6.15. Assigning Commands to slots.................................................................................................................................. 19 Section 6.16. Implementing the Remote Control......................................................................................................................... 20 Section 6.17. Implementing the Commands................................................................................................................................. 21 Section 6.18. Putting the Remote Control Through Its Paces...................................................................................................... 22 Section 6.19. Now, Let's Check Out the Execution of Our Remote Control Test......................................................................... 23 Section 6.20. Time to Write That Documentation....................................................................................................................... 25 Section 6.21. What are we Doing?................................................................................................................................................ 26 Section 6.22. Time to QA That Undo Button!.............................................................................................................................. 29 Section 6.23. Using State to Implement Undo............................................................................................................................. 30 Section 6.24. Adding Undo to the Ceiling Fan Commands.......................................................................................................... 31 Section 6.25. Get Ready to Test the Ceiling Fan.......................................................................................................................... 32 Section 6.26. Testing the Ceiling Fan........................................................................................................................................... 33 Section 6.27. Every Remote Needs a Party Mode!....................................................................................................................... 34 Section 6.28. Using a Macro Command....................................................................................................................................... 35 Section 6.29. There are no Dumb Questions................................................................................................................................ 37 Section 6.30. More Uses of the Command Pattern: Queuing Requests...................................................................................... 38 Section 6.31. More Uses of the Command Pattern: Logging Requests........................................................................................ 39 Section 6.32. Tools for your Design Toolbox............................................................................................................................... 40 Section 6.33. Exercise Solutions................................................................................................................................................... 42 Section 6.34. Exercise Solutions................................................................................................................................................... 43
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Chapter 6. Encapsulating Invocation
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Chapter 6. Encapsulating Invocation
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Chapter 6. Encapsulating Invocation
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Chapter 6. Encapsulating Invocation
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Chapter 6. Encapsulating Invocation Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 22
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Chapter 6. Encapsulating Invocation Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 23
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Chapter 6. Encapsulating Invocation Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 24
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Chapter 6. Encapsulating Invocation Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Encapsulating Invocation
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Page 25
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ME !UTOMATION OR "UST )NC
E PROGRAMMING INTERFACE FOR YOUR (OM HE FOLLOWING DESIGN AND APPLICATION SSIBLE SO THAT 7E ARE PLEASED TO PRESENT YOU WITH T REMOTE CONTROL CODE AS SIMPLE AS PO EP THE S TO KE OAL WA SIGN G ARY DE ND 0ATTERN TO !UTOMATION 2EMOTE #ONTROL /UR PRIM D WE HAVE EMPLOYED THE #OMMA NDOR CLASSES ARE PRODUCED 4O THIS EN UCE THE COST OF PRODUCING ILL RED THIS W IT DOESNT REQUIRE CHANGES AS NEW VE ELIEVE 7E B LASSES L CLASS FROM THE 6ENDOR # LOGICALLY DECOUPLE THE 2EMOTE#ONTRO OSTS UCE YOUR ONGOING MAINTENANCE C THE REMOTE AS WELL AS DRASTICALLY RED IGN UR DES W OF O VERVIE S AN O ROVIDE 4HE FOLLOWING CLASS DIAGRAM P
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Chapter 6. Encapsulating Invocation Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 26
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Chapter 6. Encapsulating Invocation Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Encapsulating Invocation
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Page 27
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Chapter 6. Encapsulating Invocation Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Encapsulating Invocation
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Page 28
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Chapter 6. Encapsulating Invocation Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Encapsulating Invocation Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 30
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Chapter 6. Encapsulating Invocation
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Chapter 6. Encapsulating Invocation Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Encapsulating Invocation
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Chapter 6. Encapsulating Invocation Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Encapsulating Invocation
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Chapter 6. Encapsulating Invocation
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Chapter 6. Encapsulating Invocation
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Chapter 6. Encapsulating Invocation Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Encapsulating Invocation
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Chapter 6. Encapsulating Invocation Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 6. Encapsulating Invocation
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Chapter 7. Being Adaptive
Table of Contents Chapter 7. Being Adaptive............................................................................ 1 Section 7.1. Adapters all around us................................................................................................................................................. 2 Section 7.2. Object oriented adapters............................................................................................................................................. 3 Section 7.3. If it walks like a duck and quacks like a duck, then it must might be a duck turkey wrapped with a duck adapter.... . . 4 Section 7.4. Test drive the adapter................................................................................................................................................. 6 Section 7.5. The Adapter Pattern explained................................................................................................................................... 7 Section 7.6. There are no Dumb Questions.................................................................................................................................... 8 Section 7.7. Adapter Pattern defined.............................................................................................................................................. 9 Section 7.8. Object and class adapters.......................................................................................................................................... 10 Section 7.9. Duck Magnets............................................................................................................................................................. 11 Section 7.10. Duck Magnets Answer............................................................................................................................................. 12 Section 7.11. Fireside Chats........................................................................................................................................................... 13 Section 7.12. Real world adapters................................................................................................................................................. 14 Section 7.13. Adapting an Enumeration to an Iterator................................................................................................................. 15 Section 7.14. Fireside Chats........................................................................................................................................................... 18 Section 7.15. And now for something different............................................................................................................................ 20 Section 7.16. Home Sweet Home Theater..................................................................................................................................... 21 Section 7.17. Watching a movie (the hard way)............................................................................................................................ 22 Section 7.18. Lights, Camera, Facade!.......................................................................................................................................... 24 Section 7.19. There are no Dumb Questions................................................................................................................................ 26 Section 7.20. Constructing your home theater facade................................................................................................................. 27 Section 7.21. Implementing the simplified interface................................................................................................................... 28 Section 7.22. Time to watch a movie (the easy way).................................................................................................................... 29 Section 7.23. Facade Pattern defined........................................................................................................................................... 30 Section 7.24. The Principle of Least Knowledge........................................................................................................................... 31 Section 7.25. How NOT to Win Friends and Influence Objects................................................................................................... 32 Section 7.26. there are no Dumb Questions................................................................................................................................. 33 Section 7.27. The Facade and the Principle of Least Knowledge................................................................................................. 35 Section 7.28. Tools for your Design Toolbox................................................................................................................................ 36 Section 7.29. Exercise solutions................................................................................................................................................... 38 Section 7.30. Exercise solutions................................................................................................................................................... 39 Section 7.31. Exercise solutions.................................................................................................................................................... 40
Chapter 7. Being Adaptive Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 1
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Chapter 7. Being Adaptive
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Chapter 7. Being Adaptive Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 25
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Page 26
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Chapter 7. Being Adaptive
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Chapter 7. Being Adaptive
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Page 29
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Page 30
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Chapter 7. Being Adaptive Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 7. Being Adaptive
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Chapter 7. Being Adaptive
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Page 33
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Page 34
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Chapter 8. Encapsulating Algorithms
Table of Contents Chapter 8. Encapsulating Algorithms.......................................................... 1 Section 8.1. It's time for some more caffeine.................................................................................................................................. 2 Section 8.2. Whipping up some coffee and tea classes (in Java)................................................................................................... 3 Section 8.3. Sir, may I abstract your Coffee, Tea?.......................................................................................................................... 6 Section 8.4. Taking the design further............................................................................................................................................ 7 Section 8.5. Abstracting prepareRecipe()...................................................................................................................................... 8 Section 8.6. What have we done?.................................................................................................................................................. 11 Section 8.7. Meet the Template Method....................................................................................................................................... 12 Section 8.8. Let's make some tea...: Behind the Scenes............................................................................................................... 13 Section 8.9. What did the Template Method get us?.................................................................................................................... 14 Section 8.10. Template Method Pattern defined.......................................................................................................................... 15 Section 8.11. Hooked on Template Method.................................................................................................................................. 18 Section 8.12. Using the hook......................................................................................................................................................... 19 Section 8.13. Let's run the TestDrive............................................................................................................................................ 20 Section 8.14. there are no Dumb Questions.................................................................................................................................. 21 Section 8.15. The Hollywood Principle......................................................................................................................................... 22 Section 8.16. The Hollywood Principle and Template Method................................................................................................... 23 Section 8.17. there are no Dumb Questions................................................................................................................................. 24 Section 8.18. Template Methods in the Wild............................................................................................................................... 25 Section 8.19. Sorting with Template Method............................................................................................................................... 26 Section 8.20. We've got some ducks to sort................................................................................................................................. 27 Section 8.21. What is compareTo()?............................................................................................................................................. 27 Section 8.22. Comparing Ducks and Ducks................................................................................................................................. 28 Section 8.23. Let's sort some Ducks............................................................................................................................................. 29 Section 8.24. The making of the sorting duck machine............................................................................................................... 30 Section 8.25. there are no Dumb Questions................................................................................................................................. 31 Section 8.26. Swingin' with Frames............................................................................................................................................. 32 Section 8.27. Applets..................................................................................................................................................................... 33 Section 8.28. Fireside Charts........................................................................................................................................................ 34 Section 8.29. Tools for your Design Toolbox................................................................................................................................ 37 Section 8.30. Exercise solutions................................................................................................................................................... 38 Section 8.31. Exercise solutions.................................................................................................................................................... 39
Chapter 8. Encapsulating Algorithms Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 8. Encapsulating Algorithms
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Chapter 8. Encapsulating Algorithms
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Chapter 8. Encapsulating Algorithms Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 8. Encapsulating Algorithms Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 8. Encapsulating Algorithms Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 9. Well-Managed Collections
Table of Contents Chapter 9. Well-Managed Collections.......................................................... 1 Section 9.1. Breaking News: Objectville Diner Merge and Objectville Pancake House................................................................ 2 Section 9.2. Check out the Menu Items.......................................................................................................................................... 3 Section 9.3. Lou and Mel's Menu implementations....................................................................................................................... 4 Section 9.4. What's the problem with having two different menu representations?.................................................................... 6 Section 9.5. Sharpen your pencil.................................................................................................................................................... 8 Section 9.6. What now?.................................................................................................................................................................. 8 Section 9.7. Can we encapsulate the iteration?.............................................................................................................................. 9 Section 9.8. Meet the Iterator Pattern........................................................................................................................................... 11 Section 9.9. Adding an Iterator to DinerMenu............................................................................................................................. 12 Section 9.10. Reworking the Diner Menu with Iterator............................................................................................................... 13 Section 9.11. Exercise..................................................................................................................................................................... 13 Section 9.12. Fixing up the Waitress code.................................................................................................................................... 14 Section 9.13. Testing our code....................................................................................................................................................... 15 Section 9.14. What have we done so far?...................................................................................................................................... 16 Section 9.15. What we have so far................................................................................................................................................. 17 Section 9.16. Making some improvements................................................................................................................................... 18 Section 9.17. There are no Dumb Questions................................................................................................................................. 18 Section 9.18. Cleaning things up with java.util.Iterator............................................................................................................... 19 Section 9.19. We are almost there................................................................................................................................................ 20 Section 9.20. What does this get us?............................................................................................................................................. 21 Section 9.21. Iterator Pattern defined.......................................................................................................................................... 22 Section 9.22. There are no Dumb Questions................................................................................................................................ 24 Section 9.23. Single Responsibility............................................................................................................................................... 25 Section 9.24. BRAIN POWER....................................................................................................................................................... 26 Section 9.25. BRAIN2 POWER..................................................................................................................................................... 26 Section 9.26. Taking a look at the Café Menu.............................................................................................................................. 28 Section 9.27. Sharpen your pencil................................................................................................................................................ 28 Section 9.28. Reworking the Café Menu code.............................................................................................................................. 29 Section 9.29. Code Up Close......................................................................................................................................................... 29 Section 9.30. Adding the Café Menu to the Waitress.................................................................................................................. 30 Section 9.31. Breakfast, lunch AND dinner.................................................................................................................................. 31 Section 9.32. What did we do?...................................................................................................................................................... 32 Section 9.33. We decoupled the Waitress.................................................................................................................................... 32 Section 9.34. ... and we made the Waitress more extensible....................................................................................................... 33 Section 9.35. But there's more!..................................................................................................................................................... 33 Section 9.36. Iterators and Collections......................................................................................................................................... 34 Section 9.37. Iterators and Collections in Java 5......................................................................................................................... 35 Section 9.38. Code Magnets.......................................................................................................................................................... 36 Section 9.39. Is the Waitress ready for prime time?.................................................................................................................... 37 Section 9.40. Just when we thought it was safe........................................................................................................................... 39 Section 9.41. What do we need?................................................................................................................................................... 40 Section 9.42. The Composite Pattern defined.............................................................................................................................. 42 Section 9.43. Designing Menus with Composite.......................................................................................................................... 45 Section 9.44. Implementing the Menu Component..................................................................................................................... 46 Section 9.45. Implementing the Menu Item................................................................................................................................. 47 Section 9.46. Implementing the Composite Menu...................................................................................................................... 48 Section 9.47. Getting ready for a test drive.................................................................................................................................. 50 Section 9.48. Now for the test drive.............................................................................................................................................. 51 Section 9.49. Getting ready for a test drive.................................................................................................................................. 52 Section 9.50. Flashback to Iterator............................................................................................................................................... 54 Section 9.51. The Composite Iterator........................................................................................................................................... 55 Section 9.52. The Null Iterator..................................................................................................................................................... 58 Section 9.53. Give me the vegetarian menu................................................................................................................................. 59 Section 9.54. The magic of Iterator & Composite together.......................................................................................................... 60 Section 9.55. Patterns Exposed..................................................................................................................................................... 62 Section 9.56. WHO DOES WHAT?............................................................................................................................................... 65
Chapter 9. Well-Managed Collections Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 9. Well-Managed Collections
Section 9.57. Tools for your Design Toolbox................................................................................................................................ 66 Section 9.58. Exercise solutions................................................................................................................................................... 67 Section 9.59. Code Magnets Solution........................................................................................................................................... 68 Section 9.60. WHO DOES WHAT?.............................................................................................................................................. 69 Section 9.61. Exercise Solution..................................................................................................................................................... 70
Chapter 9. Well-Managed Collections Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 9. Well-Managed Collections
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Chapter 9. Well-Managed Collections
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Chapter 9. Well-Managed Collections Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 9. Well-Managed Collections Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 9. Well-Managed Collections
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Chapter 10. The State of Things
Table of Contents Chapter 10. The State of Things................................................................... 1 Section 10.1. Java Breakers............................................................................................................................................................. 2 Section 10.2. Cubicle Conversation................................................................................................................................................ 3 Section 10.3. State machines 101.................................................................................................................................................... 4 Section 10.4. Writing the code........................................................................................................................................................ 6 Section 10.5. In-house testing......................................................................................................................................................... 8 Section 10.6. You knew it was coming... a change request!.......................................................................................................... 10 Section 10.7. Design Puzzle............................................................................................................................................................ 11 Section 10.8. The messy STATE of things..................................................................................................................................... 12 Section 10.9. The new design........................................................................................................................................................ 14 Section 10.10. Defining the State interfaces and classes.............................................................................................................. 15 Section 10.11. Implementing our State classes.............................................................................................................................. 17 Section 10.12. Reworking the Gumball Machine.......................................................................................................................... 18 Section 10.13. Implementing more states.................................................................................................................................... 20 Section 10.14. Let's take a look at what we've done so far............................................................................................................ 23 Section 10.15. Sharpen your pencil............................................................................................................................................... 25 Section 10.16. The State Pattern defined...................................................................................................................................... 26 Section 10.17. there are no Dumb Questions................................................................................................................................ 28 Section 10.18. We still need to finish the Gumball 1 in 10 game.................................................................................................. 29 Section 10.19. Finishing the game................................................................................................................................................ 30 Section 10.20. Demo for the CEO of Mighty Gumball, Inc.......................................................................................................... 31 Section 10.21. there are no Dumb Questions............................................................................................................................... 32 Section 10.22. Sanity check........................................................................................................................................................... 33 Section 10.23. We almost forgot!.................................................................................................................................................. 36 Section 10.24. Sharpen your pencil.............................................................................................................................................. 37 Section 10.25. Tools for your Design Toolbox.............................................................................................................................. 39 Section 10.26. Exercise solutions................................................................................................................................................. 40 Section 10.27. Exercise solutions.................................................................................................................................................. 41
Chapter 10. The State of Things Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 10. The State of Things
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Chapter 10. The State of Things
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Chapter 10. The State of Things
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Chapter 10. The State of Things Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 10. The State of Things Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 10. The State of Things Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 10. The State of Things Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 10. The State of Things
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Chapter 10. The State of Things Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 10. The State of Things
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Chapter 10. The State of Things
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Chapter 10. The State of Things
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Chapter 10. The State of Things
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Chapter 10. The State of Things
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Page 29
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Chapter 10. The State of Things
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Page 30
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Page 31
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Chapter 10. The State of Things
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Page 32
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Chapter 10. The State of Things Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 34
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Page 35
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Page 36
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Chapter 10. The State of Things
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Page 37
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Chapter 10. The State of Things Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 10. The State of Things
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Chapter 10. The State of Things
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Chapter 10. The State of Things
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Chapter 10. The State of Things Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 10. The State of Things Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access
Table of Contents Chapter 11. Controlling Object Access.......................................................... 1 Section 11.1. Coding the Monitor.................................................................................................................................................... 3 Section 11.2. Testing the Monitor................................................................................................................................................... 4 Section 11.3. The role of the 'remote proxy'.................................................................................................................................... 6 Section 11.4. Adding a remote proxy to the Gumball Machine monitoring code.......................................................................... 8 Section 11.5. Remote methods 101.................................................................................................................................................. 9 Section 11.6. How the method call happens................................................................................................................................. 10 Section 11.7. Java RMI, the Big Picture......................................................................................................................................... 12 Section 11.8. Making the Remote service...................................................................................................................................... 13 Section 11.9. Step one: make a Remote interface.......................................................................................................................... 14 Section 11.10. Step two: make a Remote implementation............................................................................................................ 15 Section 11.11. Step three: generate stubs and skeletons............................................................................................................... 16 Section 11.12. Step four: run rmiregistry....................................................................................................................................... 16 Section 11.13. Step five: start the service....................................................................................................................................... 16 Section 11.14. How does the client get the stub object?................................................................................................................ 18 Section 11.15. Watch it................................................................................................................................................................... 21 Section 11.16. Back to our GumballMachine remote proxy.......................................................................................................... 22 Section 11.17. Getting the GumballMachine ready to be a remote service.................................................................................. 23 Section 11.18. Registering with the RMI registry......................................................................................................................... 25 Section 11.19. Now for the GumballMonitor client...................................................................................................................... 26 Section 11.20. Writing the Monitor test drive............................................................................................................................... 27 Section 11.21. Another demo for the CEO of Mighty Gumball..................................................................................................... 28 Section 11.22. And now let's put the monitor in the hands of the CEO. Hopefully this time he'll love it:.................................. 29 Section 11.23. Behind the Scenes.................................................................................................................................................. 30 Section 11.24. The Proxy Pattern defined..................................................................................................................................... 32 Section 11.25. Get ready for Virtual Proxy.................................................................................................................................... 34 Section 11.26. Displaying CD covers............................................................................................................................................. 35 Section 11.27. Designing the CD cover Virtual Proxy................................................................................................................... 36 Section 11.28. Writing the Image Proxy........................................................................................................................................ 37 Section 11.29. Design Puzzle......................................................................................................................................................... 40 Section 11.30. Testing the CD Cover Viewer................................................................................................................................. 41 Section 11.31. What did we do?: Behin the scenes........................................................................................................................ 42 Section 11.32. there are no Dumb Questions................................................................................................................................ 43 Section 11.33. Fireside Charts....................................................................................................................................................... 44 Section 11.34. Using the Java API's Proxy to create a protection proxy...................................................................................... 46 Section 11.35. Matchmaking in Objectville................................................................................................................................... 47 Section 11.36. The PersonBean implementation.......................................................................................................................... 48 Section 11.37. Five minute drama: protecting subjects................................................................................................................ 50 Section 11.38. Big Picture: creating a Dynamic Proxy for the PersonBean.................................................................................. 51 Section 11.39. Step one: creating Invocation Handlers................................................................................................................ 52 Section 11.40. Creating Invocation Handlers continued.............................................................................................................. 53 Section 11.41. Exercise................................................................................................................................................................... 54 Section 11.42. Step two: creating the Proxy class and instantiating the Proxy object................................................................. 55 Section 11.43. Sharpen your pencil............................................................................................................................................... 55 Section 11.44. Testing the matchmaking service.......................................................................................................................... 56 Section 11.45. Running the code................................................................................................................................................... 57 Section 11.46. there are no Dumb Questions................................................................................................................................ 58 Section 11.47. WHO DOES WHAT............................................................................................................................................... 59 Section 11.48. The Proxy Zoo........................................................................................................................................................ 60 Section 11.49. Tools for your Design Toolbox.............................................................................................................................. 63 Section 11.50. Exercise solutions.................................................................................................................................................. 64 Section 11.51. Exercise solutions................................................................................................................................................... 65 Section 11.52. Ready-bake Code: The code for the CD Cover Viewer.......................................................................................... 66 Section 11.53. Ready-bake Code: The code for the CD Cover Viewer, continued........................................................................ 68
Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access
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Chapter 11. Controlling Object Access
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access
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Chapter 11. Controlling Object Access
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access
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Chapter 11. Controlling Object Access
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access
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Chapter 11. Controlling Object Access
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 38
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 39
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 40
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 41
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 42
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 43
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4HE 2EMOTE 0ROXY AND 6IRTUAL 0ROXY SEEM SO DIFFERENT TO ME ARE THEY REALLY /.% PATTERN
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9OULL lND A LOT OF VARIANTS OF THE 0ROXY 0ATTERN IN THE REAL WORLD WHAT THEY ALL HAVE IN COMMON IS THAT THEY INTERCEPT A METHOD INVOCATION THAT THE CLIENT IS MAKING ON THE SUBJECT 4HIS LEVEL OF INDIRECTION ALLOWS US TO DO MANY THINGS INCLUDING DISPATCHING REQUESTS TO A REMOTE SUBJECT PROVIDING A REPRESENTATIVE FOR AN EXPENSIVE OBJECT AS IT IS CREATED OR AS YOULL SEE PROVIDING SOME LEVEL OF PROTECTION THAT CAN DETERMINE WHICH CLIENTS SHOULD BE CALLING WHICH METHODS 4HATS JUST THE BEGINNING THE GENERAL 0ROXY 0ATTERN CAN BE APPLIED IN MANY DIFFERENT WAYS AND WELL COVER SOME OF THE OTHER WAYS AT THE END OF THE CHAPTER
Q:
)MAGE0ROXY SEEMS JUST LIKE A $ECORATOR TO ME ) MEAN WE ARE BASICALLY WRAPPING ONE OBJECT WITH ANOTHER AND THEN DELEGATING THE CALLS TO THE )MAGE)CON 7HAT AM ) MISSING
A:
3OMETIMES 0ROXY AND $ECORATOR LOOK VERY SIMILAR BUT THEIR PURPOSES ARE DIFFERENT A DECORATOR ADDS BEHAVIOR TO A CLASS WHILE A PROXY CONTROLS ACCESS TO IT 9OU MIGHT SAY h)SNT THE LOADING MESSAGE ADDING BEHAVIOR v )N SOME
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(OW DO ) MAKE CLIENTS USE THE 0ROXY RATHER THAN THE 2EAL 3UBJECT
A:
'OOD QUESTION /NE COMMON TECHNIQUE IS TO PROVIDE A FACTORY THAT INSTANTIATES AND RETURNS THE SUBJECT "ECAUSE THIS HAPPENS IN A FACTORY METHOD WE CAN THEN WRAP THE SUBJECT WITH A PROXY BEFORE RETURNING IT 4HE CLIENT NEVER KNOWS OR CARES THAT ITS USING A PROXY INSTEAD OF THE REAL THING
Q:
) NOTICED IN THE )MAGE0ROXY EXAMPLE YOU ALWAYS CREATE A NEW )MAGE)CON TO GET THE IMAGE EVEN IF THE IMAGE HAS ALREADY BEEN RETRIEVED #OULD YOU IMPLEMENT SOMETHING SIMILAR TO THE )MAGE0ROXY THAT CACHES PAST RETRIEVALS
A:
9OU ARE TALKING ABOUT A SPECIAL IZED FORM OF A 6IRTUAL 0ROXY CALLED A #ACHING 0ROXY ! CACHING PROXY MAINTAINS A CACHE OF PREVIOUS CREATED OBJECTS AND WHEN A REQUEST IS MADE IT RETURNS CACHED OBJECT IF POSSIBLE 7ERE GOING TO LOOK THIS AND AT SEVERAL OTHER VARIANTS OF THE 0ROXY 0ATTERN AT THE END OF THE CHAPTER
Q:
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A:
"OTH 0ROXY AND !DAPTER SIT IN FRONT OF OTHER OBJECTS AND FORWARD REQUESTS TO THEM 2EMEMBER THAT !DAPTER CHANGES THE INTERFACE OF THE OBJECTS IT ADAPTS WHILE THE 0ROXY IMPLEMENTS THE SAME INTERFACE 4HERE IS ONE ADDITIONAL SIMILARITY THAT RELATES TO THE 0ROTECTION 0ROXY ! 0ROTECTION 0ROXY MAY ALLOW OR DISALLOW A CLIENT ACCESS TO PARTICULAR METHODS IN AN OBJECT BASED ON THE ROLE OF THE CLIENT )N THIS WAY A 0ROTECTION 0ROXY MAY ONLY PROVIDE A PARTIAL INTERFACE TO A CLIENT WHICH IS QUITE SIMILAR TO SOME !DAPTERS 7E ARE GOING TO TAKE A LOOK AT 0ROTECTION 0ROXY IN A FEW PAGES
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Chapter 11. Controlling Object Access Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 44
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Chapter 12. Patterns of Patterns
Table of Contents Chapter 12. Patterns of Patterns.................................................................. 1 Section 12.1. Working together....................................................................................................................................................... 2 Section 12.2. Duck reunion............................................................................................................................................................. 3 Section 12.3. There are no Dumb Questions................................................................................................................................ 24 Section 12.4. What did we do?...................................................................................................................................................... 25 Section 12.5. A bird's duck's eye view: the class diagram............................................................................................................. 26 Section 12.6. The King of Compound Patterns............................................................................................................................ 28 Section 12.7. Meet the Model-View-Controller............................................................................................................................. 31 Section 12.8. A closer look............................................................................................................................................................ 32 Section 12.9. There are no Dumb Questions................................................................................................................................ 33 Section 12.10. Looking at MVC through patterns-colored glasses............................................................................................... 34 Section 12.11. Using MVC to control the beat............................................................................................................................... 36 Section 12.12. Meet the Java DJ View.......................................................................................................................................... 36 Section 12.13. Putting the pieces together.................................................................................................................................... 38 Section 12.14. Building the pieces................................................................................................................................................. 39 Section 12.15. Now let's have a look at the concrete BeatModel class:........................................................................................ 40 Section 12.16. The View................................................................................................................................................................. 41 Section 12.17. BRAIN POWER...................................................................................................................................................... 41 Section 12.18. Implementing the View......................................................................................................................................... 42 Section 12.19. Implementing the View, continued....................................................................................................................... 43 Section 12.20. Now for the Controller.......................................................................................................................................... 44 Section 12.21. And here's the implementation of the controller:................................................................................................. 45 Section 12.22. Putting it all together............................................................................................................................................ 46 Section 12.23. And now for a test run........................................................................................................................................... 46 Section 12.24. Exploring Strategy................................................................................................................................................. 47 Section 12.25. Adapting the Model............................................................................................................................................... 48 Section 12.26. Now we're ready for a HeartController................................................................................................................. 49 Section 12.27. And now for a test run........................................................................................................................................... 50 Section 12.28. MVC and the Web.................................................................................................................................................. 51 Section 12.29. Model 2 is more than just a clean design.............................................................................................................. 52 Section 12.30. Model 2: DJ'ing from a cell phone........................................................................................................................ 53 Section 12.31. Now we need a view............................................................................................................................................... 56 Section 12.32. Putting Model 2 to the test.................................................................................................................................... 57 Section 12.33. Design Patterns and Model 2................................................................................................................................ 59 Section 12.34. Observer................................................................................................................................................................. 59 Section 12.35. Strategy.................................................................................................................................................................. 60 Section 12.36. There are no Dumb Questions............................................................................................................................... 61 Section 12.37. Tools for your Design Toolbox.............................................................................................................................. 62 Section 12.38. Exercise solutions.................................................................................................................................................. 63 Section 12.39. Ready-bake Code................................................................................................................................................... 66 Section 12.40. Ready-bake Code: The View................................................................................................................................. 70 Section 12.41. The Controller........................................................................................................................................................ 73 Section 12.42. The Heart Model.................................................................................................................................................... 75 Section 12.43. The Heart Adapter................................................................................................................................................. 77 Section 12.44. The Controller....................................................................................................................................................... 78
Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns
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Page 11
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 12
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 13
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns
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Page 14
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns
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Page 15
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns
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Chapter 12. Patterns of Patterns
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns
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Page 22
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Chapter 12. Patterns of Patterns
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Chapter 12. Patterns of Patterns
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Chapter 12. Patterns of Patterns
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Page 25
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 12. Patterns of Patterns Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World
Table of Contents Chapter 13. Patterns in the Real World........................................................ 1 Section 13.1. Design Pattern defined.............................................................................................................................................. 3 Section 13.2. Looking more closely at the Design Pattern definition............................................................................................ 5 Section 13.3. Geek Bits.................................................................................................................................................................... 6 Section 13.4. there are no Dumb Questions.................................................................................................................................. 10 Section 13.5. So you wanna be a Design Patterns writer............................................................................................................... 11 Section 13.6. Organizing Design Patterns..................................................................................................................................... 13 Section 13.7. Solution: Pattern Categories.................................................................................................................................... 14 Section 13.8. there are no Dumb Questions.................................................................................................................................. 15 Section 13.9. Thinking in Patterns................................................................................................................................................ 18 Section 13.10. Your Mind on Patterns........................................................................................................................................... 21 Section 13.11. Don't forget the power of the shared vocabulary................................................................................................... 23 Section 13.12. Cruisin' Object ville with the Gang of Four........................................................................................................... 25 Section 13.13. Your journey has just begun.................................................................................................................................. 26 Section 13.14. The Patterns Zoo.................................................................................................................................................... 28 Section 13.15. Annihilating evil with Anti-Patterns..................................................................................................................... 30 Section 13.16. Tools for your Design Toolbox.............................................................................................................................. 32 Section 13.17. Leaving Objectville................................................................................................................................................. 33 Section 13.18. Exercise solutions.................................................................................................................................................. 34
Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 19
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Page 28
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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Chapter 13. Patterns in the Real World
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Chapter 13. Patterns in the Real World Head First Design Patterns By Eric Freeman, Elisabeth Freeman, Bert Bates, Kathy Sierra Prepared for Ann Cherkis, Safari ID: [email protected] ISBN: 0596007124 Publisher: O'Reilly Print Publication Date: 2004/10/25 User number: 1673621 Copyright 2008, Safari Books Online, LLC. This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.
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