设计模式：装饰模式(Head First版)
装饰者模式：动态地将责任附加到对象上，若到扩展功能，装饰者提供了比继承更有弹性的替代方案。
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UML图
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有这样一个需求，咖啡店出售各式咖啡，如深焙、低卡、摩卡等，也有各种调料，如牛奶、奶泡等。
咖啡店需要根据咖啡中所放入的不同调料收取不同的费用。用装饰者模式来实现
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定义一个抽象组件
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package com.headfirst.chapter3;/** * 定义了一个抽象类，用于表示组件，它定义了一个抽象方法cost */public abstract class Beverage {String description; public String getDescription() {return description;}public abstract double cost();//计费方法}?
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下面两个是具体组件，也就是被装饰者
1,深焙咖啡
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package com.headfirst.chapter3;public class DarkRoast extends Beverage {//深焙咖啡public DarkRoast() {this.description = "DarkRoast";}public double cost() {return 0.89;}}?
2,混合咖啡
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package com.headfirst.chapter3;public class HouseBlend extends Beverage {public HouseBlend() {this.description = "HouseBlend";}public double cost() {return 1.89;}}?
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装饰者
这里定义了一个抽象方法getDescription，那么子类必须它来增加描述
如Houseblend Milk
package com.headfirst.chapter3;public abstract class CondimentDecorator extends Beverage {public abstract String getDescription();}??
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?下面两个是装饰者
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package com.headfirst.chapter3;public class Milk extends CondimentDecorator {private Beverage beverage;//这个引用指向被装饰者public Milk(Beverage beverage) {this.beverage = beverage;}public String getDescription() {return beverage.getDescription() + " Milk";}public double cost() {return beverage.cost() + 0.20;}}?
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package com.headfirst.chapter3;public class Mocha extends Beverage {Beverage beverage;public Mocha(Beverage beverage) {this.beverage = beverage;}public String getDescription() {return beverage.getDescription() + " Mocha";}public double cost() {return beverage.cost()+0.59;}}??
测试类：
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package com.headfirst.chapter3;public class Test {public static void main(String[] args) {Beverage darkRoast = new DarkRoast();darkRoast = new Mocha(darkRoast);darkRoast = new Milk(darkRoast);System.out.println(darkRoast.getDescription()+" $"+darkRoast.cost());}}?最后打印出：DarkRoast Mocha Milk $1.68
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