装饰器模式

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装饰器模式动态地将责任附加到对象上。想要扩展功能，装饰器提供于继承有别的另一种选择

java类图

这里写图片描述

java代码

// 饮料抽象类public abstract class Beverage {    protected String description = "Beverage";    public String getDescription() {        return description;    }    public abstract double cost();}// 烘焙咖啡public class DarkRoast extends Beverage {    public DarkRoast() {        description = "Dark Roast Coffee";    }    @Override    public double cost() {        return 0.99;    }}// 低咖啡因咖啡public class Decaf extends Beverage {    public Decaf() {        description = "Decaf Coffee";    }    @Override    public double cost() {        return 1.05;    }}// 浓缩咖啡public class Espresso extends Beverage {    public Espresso() {        description = "Espresso Coffee";    }    @Override    public double cost() {        return 1.99;    }}// 混合咖啡public class HouseBlend extends Beverage {    public HouseBlend() {        description = "House Blend Coffee";    }    @Override    public double cost() {        return 0.89;    }}// 配料装饰器public abstract class CondimentDecorator extends Beverage {    public abstract String getDescription();}// 牛奶配料public class Milk extends CondimentDecorator {    private Beverage beverage;    public Milk(Beverage beverage) {        this.beverage = beverage;    }    @Override    public String getDescription() {        return beverage.getDescription() + " ,Milk";    }    @Override    public double cost() {        return beverage.cost() + 0.1;    }}// 摩卡配料public class Mocha extends CondimentDecorator {    private Beverage beverage;    public Mocha(Beverage beverage) {        this.beverage = beverage;    }    @Override    public String getDescription() {        return beverage.getDescription() + " ,Mocha";    }    @Override    public double cost() {        return beverage.cost() + 0.2;    }}// 豆浆配料public class Soy extends CondimentDecorator {    private Beverage beverage;    public Soy(Beverage beverage) {        this.beverage = beverage;    }    @Override    public String getDescription() {        return beverage.getDescription() + " ,Soy";    }    @Override    public double cost() {        return beverage.cost() + 0.15;    }}// 奶泡配料public class Whip extends CondimentDecorator {    private Beverage beverage;    public Whip(Beverage beverage) {        this.beverage = beverage;    }    @Override    public String getDescription() {        return beverage.getDescription() + " ,Whip";    }    @Override    public double cost() {        return beverage.cost() + 0.1;    }}// 测试类public class Test {    public static void main(String[] args) {        new Test().test();    }    private void test() {        Beverage espresso = new Espresso();        System.out.println(espresso.getDescription() + "  $" + espresso.cost());        Beverage darkRoast = new DarkRoast();        darkRoast = new Mocha(darkRoast);        darkRoast = new Mocha(darkRoast);        darkRoast = new Whip(darkRoast);        System.out.println(darkRoast.getDescription() + "  $" + darkRoast.cost());        Beverage houseBlend = new HouseBlend();        houseBlend = new Soy(houseBlend);        houseBlend = new Mocha(houseBlend);        houseBlend = new Whip(houseBlend);        System.out.println(houseBlend.getDescription() + "  $" + houseBlend.cost());    }}

注：

装饰者模式意味着一群装饰者类，这些类用来包装具体组件。
装饰者反映出被装饰者的类型（事实上，他们具有相同的类型，都经过接口或者继承实现）。
装饰者可以在被装饰者的行为前面/或后面加上自己的行为，甚至将被装饰者的行为整个取代掉，而达到特定的目的。
你可以用无数个装饰者包装一个组件。
装饰者一般对组件的客户是透明的，除非客户程序依赖于组件的具体类型。
装饰者会导致设计中出现许多小对象，如果过度使用，会让程序变得很复杂。

参考文章
Head First 设计模式

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