java 装饰者模式

在First Head 设计模式一书中，
有这样一个例子。

在装饰者模式中，有组件类，装饰器，由此可以逐渐添加类的功能，就好像俄罗斯套娃。

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package tablejava;/* * 以下是组件类 *  * *///抽象组件abstract class Beverage{    protected String description="Unknow Beverage";    public String getDescription() {        return description;    }    public abstract double cost() ;}//具体组件class Espresso extends Beverage{    public Espresso() {        super();        description="Espresso";    }    @Override    public double cost() {        return 1.99;    }}class HouseBlend extends Beverage{    public HouseBlend() {        super();        description="House Blend Coffee";    }    @Override    public double cost() {        return 0.89;    }}/* *  *以下的类都是装饰者 *  * *///抽象装饰者类abstract class CondimentDecorator extends Beverage{    public abstract String getDescription();}//具体装饰者类class Mocha extends CondimentDecorator{    Beverage beverage;    public Mocha(Beverage beverage) {        super();        this.beverage = beverage;    }    @Override    public String getDescription() {        return this.beverage.getDescription()+" , Mocha";    }    @Override    public double cost() {        return 0.20+this.beverage.cost();    }}class Soy extends CondimentDecorator{    Beverage beverage;    public Soy(Beverage beverage) {        super();        this.beverage = beverage;    }    @Override    public String getDescription() {        return this.beverage.getDescription()+" , Soy";    }    @Override    public double cost() {        return 0.30+this.beverage.cost();    }}class Whip extends CondimentDecorator{    Beverage beverage;    public Whip(Beverage beverage) {        super();        this.beverage = beverage;    }    @Override    public String getDescription() {        return this.beverage.getDescription()+" , Whip";    }    @Override    public double cost() {        return 0.40+this.beverage.cost();    }}public class Decorator {    public static void main(String[] args) {        Beverage beverage=new Espresso();        System.out.println(beverage.getDescription()+" $ "+beverage.cost());        beverage=new Soy(beverage);        System.out.println(beverage.getDescription()+" $ "+beverage.cost());        beverage=new Mocha(beverage);        System.out.println(beverage.getDescription()+" $ "+beverage.cost());        beverage=new Whip(beverage);        System.out.println(beverage.getDescription()+" $ "+beverage.cost());        System.out.println("----------------------------------------------");        Beverage beverage2=new HouseBlend();        System.out.println(beverage2.getDescription()+" $ "+beverage2.cost());        beverage2=new Soy(beverage2);        System.out.println(beverage2.getDescription()+" $ "+beverage2.cost());        beverage2=new Mocha(beverage2);        System.out.println(beverage2.getDescription()+" $ "+beverage2.cost());        beverage2=new Whip(beverage2);        System.out.println(beverage2.getDescription()+" $ "+beverage2.cost());    }}

运行结果为：

Espresso $ 1.99Espresso , Soy $ 2.29Espresso , Soy , Mocha $ 2.49Espresso , Soy , Mocha , Whip $ 2.89----------------------------------------------House Blend Coffee $ 0.89House Blend Coffee , Soy $ 1.19House Blend Coffee , Soy , Mocha $ 1.39House Blend Coffee , Soy , Mocha , Whip $ 1.79

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在这个例子中，如果按照刚刚的图例来理解，
就会得到: