The Decorator Pattern

Transcript

1. The Decorator Pattern Matt Steele
2. What is it? ❖ In object-oriented programming, the decorator pattern (also known as Wrapper, an alternative naming shared with the Adapter pattern) is a design pattern that allows behavior to be added to an individual object, either statically or dynamically, without affecting the behavior of other objects from the same class.! ❖ - Wikipedia
3. Give it to me straight, nerd.
4. –Me, right now “The Decorator Pattern lets you implement the Open Closed Principle”
5. https://flic.kr/p/awnCQu The Open-Closed Principle Open to Extension, Closed to Modification
6. Version 1: Inheritance
8. https://flic.kr/p/aYVKBx Version 2: Decorator
10. New Behavior, New Decorator
11. https://flic.kr/p/9tT9Yh Nest ‘em
12. Original public static class MacBook { public int cost() { return 997; } ! public double screenSize() { return 11.6; } }
13. Nest 1 public static class Memory extends MacBook { private MacBook device; ! public Memory(MacBook device) { this.device = device; } @Override public int cost() { return device.cost() + 75; } }
14. Nest 2 public static class Engraving extends MacBook { private MacBook device; ! public Engraving(MacBook device) { this.device = device; } @Override public int cost() { return device.cost() + 200; } }
15. Nest 3 public static class Insurance extends MacBook { private MacBook device; ! public Insurance(MacBook device) { this.device = device; } ! @Override public int cost() { return device.cost() + 250; } }
16. Running public static void main(String[] args) { MacBook book = new MacBook(); ! MacBook withFeatures = new Insurance(new Engraving(new Memory(book))); System.out.println(withFeatures.cost()); }
18. Nesting https://flic.kr/p/4PTTW5
19. Isn’t Inheritance evil?
20. - Me, again “Types, not behavior”
21. JavaScript function MacBook() { this.cost = function () { return 997; }; this.screenSize = function () { return 11.6; }; }
22. Nest 1 function memory( macbook ) { var v = macbook.cost(); macbook.cost = function() { return v + 75; }; }
23. Nest 2 function engraving( macbook ){ var v = macbook.cost(); macbook.cost = function() { return v + 200; }; }
24. Nest 3 function insurance( macbook ){ var v = macbook.cost(); macbook.cost = function() { return v + 250; }; }
25. Running var mb = new MacBook(); memory( mb ); engraving( mb ); insurance( mb ); ! console.log(mb.cost());
26. https://flic.kr/p/H6Q6w Nesting
27. Uses
29. Logging
30. Logging Performance
31. Logging Performance Security
32. Logging Performance Security Transactions
33. Logging Performance Security Transactions (anything AOP can do)
34. Logging Performance Security Transactions (anything AOP can do)
35. Example: Spring JMS http://docs.spring.io/spring/docs/3.2.8.RELEASE/javadoc-api/org/springframework/jms/connection/package-frame.html
36. Summary
37. Summary ❖ Open-Closed Principle
38. Summary ❖ Open-Closed Principle ❖ Decorator Pattern: Alternative to Inheritance
39. Summary ❖ Open-Closed Principle ❖ Decorator Pattern: Alternative to Inheritance ❖ Decorators mirror type
40. Summary ❖ Open-Closed Principle ❖ Decorator Pattern: Alternative to Inheritance ❖ Decorators mirror type ❖ Adds new functionality around (or in place of) base
41. Summary ❖ Open-Closed Principle ❖ Decorator Pattern: Alternative to Inheritance ❖ Decorators mirror type ❖ Adds new functionality around (or in place of) base ❖ Wrap with 0 or more decorators
42. Summary ❖ Open-Closed Principle ❖ Decorator Pattern: Alternative to Inheritance ❖ Decorators mirror type ❖ Adds new functionality around (or in place of) base ❖ Wrap with 0 or more decorators ❖ Transparent, should be orderless
43. Summary ❖ Open-Closed Principle ❖ Decorator Pattern: Alternative to Inheritance ❖ Decorators mirror type ❖ Adds new functionality around (or in place of) base ❖ Wrap with 0 or more decorators ❖ Transparent, should be orderless ❖ Make sure you’re logging usage well
44. https://flic.kr/p/4ryZqa