The Decorator Pattern - Speaker Deck

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The Decorator Pattern Matt Steele

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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

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Give it to me straight, nerd.

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–Me, right now “The Decorator Pattern lets you implement the Open Closed Principle”

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https://ﬂic.kr/p/awnCQu The Open-Closed Principle Open to Extension, Closed to Modiﬁcation

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Version 1: Inheritance

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https://ﬂic.kr/p/aYVKBx Version 2: Decorator

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New Behavior, New Decorator

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https://ﬂic.kr/p/9tT9Yh Nest ‘em

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Original public static class MacBook { public int cost() { return 997; } ! public double screenSize() { return 11.6; } }

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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; } }

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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; } }

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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; } }

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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()); }

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Nesting https://ﬂic.kr/p/4PTTW5

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Isn’t Inheritance evil?

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- Me, again “Types, not behavior”

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JavaScript function MacBook() { this.cost = function () { return 997; }; this.screenSize = function () { return 11.6; }; }

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Nest 1 function memory( macbook ) { var v = macbook.cost(); macbook.cost = function() { return v + 75; }; }

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Nest 2 function engraving( macbook ){ var v = macbook.cost(); macbook.cost = function() { return v + 200; }; }

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Nest 3 function insurance( macbook ){ var v = macbook.cost(); macbook.cost = function() { return v + 250; }; }

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Running var mb = new MacBook(); memory( mb ); engraving( mb ); insurance( mb ); ! console.log(mb.cost());

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https://ﬂic.kr/p/H6Q6w Nesting

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Uses

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Logging

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Logging Performance

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Logging Performance Security

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Logging Performance Security Transactions

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Logging Performance Security Transactions (anything AOP can do)

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Logging Performance Security Transactions (anything AOP can do)

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Example: Spring JMS http://docs.spring.io/spring/docs/3.2.8.RELEASE/javadoc-api/org/springframework/jms/connection/package-frame.html

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Summary

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Summary ❖ Open-Closed Principle

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Summary ❖ Open-Closed Principle ❖ Decorator Pattern: Alternative to Inheritance

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Summary ❖ Open-Closed Principle ❖ Decorator Pattern: Alternative to Inheritance ❖ Decorators mirror type

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Summary ❖ Open-Closed Principle ❖ Decorator Pattern: Alternative to Inheritance ❖ Decorators mirror type ❖ Adds new functionality around (or in place of) base

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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