Head First 设计模式学习笔记（三）装饰者模式
装饰者模式：动态地将责任附加到对象上。若要扩展功能，装饰者提供了比继承更有弹性的替代方案。
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通常装饰者模式是采用抽象类，但也可以使用接口，装饰者和装饰对象均继承同一个抽象类。在这里，我们利用继承达到“类型匹配”。
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package com.coffee;/* * 饮料类 */public abstract class Beverage {String description = "Unknown Beverage";public String getDescription() {return description;}public abstract double cost();}?package com.coffee;/* * 装饰者类 */public abstract class CondimentDecorator extends Beverage {public abstract String getDescription();}?package com.coffee;/* * 具体的饮料：浓缩咖啡 */public class Espresso extends Beverage {public Espresso() {description = "Espresso";}public double cost() {return 1.99;}}?package com.coffee;/* * 具体的饮料：HouseBlend 咖啡 */public class HouseBlend extends Beverage {public HouseBlend() {description = "House Blend Coffee";}public double cost() {return .89;}}?package com.coffee;/* * 具体的调料： 摩卡 */public class Mocha extends CondimentDecorator {Beverage beverage;public Mocha(Beverage beverage) {this.beverage = beverage;}public String getDescription() {return beverage.getDescription() + ", Mocha";}public double cost() {return .20 + beverage.cost();}}?package com.coffee;/* * 测试类 */public class StarbuzzCoffee {public static void main(String args[]) {Beverage beverage = new Espresso();System.out.println(beverage.getDescription() + " $" + beverage.cost());Beverage beverage2 = new Mocha(beverage);System.out.println(beverage2.getDescription() + " $" + beverage2.cost());}}