Head First 装饰者模式

最新推荐文章于 2024-12-20 13:55:30 发布

转载最新推荐文章于 2024-12-20 13:55:30 发布 · 48 阅读

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CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/wwwx/p/9530384.html

本文深入解析装饰者模式，通过饮料类及其调料的具体实现，展示如何动态地为对象添加职责，而不破坏原有的类结构。适用于需要扩展类功能或给对象增加可撤销功能的场景。

一、类图

二、示例代码

类图：

　　代码：

1、饮料类

/**
 * 饮料类
 */
public abstract class Beverage {

    public String  description = "Unknown Beverage";

    public String getDescription(){
        return description;
    }

    public abstract double cost();

}

　　2、具体饮料类

public class Espresso extends Beverage {

    public Espresso() {
        description = "Espresso";
    }

    @Override
    public double cost() {
        return 1.99;
    }
}


public class HouseBlend extends Beverage {

    public HouseBlend() {
        description = "House Blend Coffee";
    }

    @Override
    public double cost() {
        return 0.89;
    }
}

　　3、调料类，必须让CondimentDecorator能够取代Beverage，所以将CondimentDecorator扩展自Beverage

/**
 * 调料类
 */
public abstract class CondimentDecorator extends Beverage{

    public abstract String  getDescription();

}

　　4、具体调料类

public class Mocha extends CondimentDecorator {

    Beverage beverage;

    public Mocha(Beverage beverage) {
        this.beverage = beverage;
    }

    @Override
    public String getDescription() {
        return beverage.getDescription() + ", Mocha";
    }

    @Override
    public double cost() {
        return 0.2 + beverage.cost();
    }
}



public class Soy extends CondimentDecorator {

    Beverage beverage;

    public Soy(Beverage beverage) {
        this.beverage = beverage;
    }

    @Override
    public String getDescription() {
        return beverage.getDescription() + ", Soy";
    }

    @Override
    public double cost() {
        return 0.3 + beverage.cost();
    }
    
}



public class Whip extends CondimentDecorator {

    Beverage beverage;

    public Whip(Beverage beverage) {
        this.beverage = beverage;
    }

    @Override
    public String getDescription() {
        return beverage.getDescription() + ", Whip";
    }

    @Override
    public double cost() {
        return 0.4 + beverage.cost();
    }
}

　　5、订单测试类

/**
 * 咖啡供应类
 */

public class StarbuzzCoffee {

    public static void main(String[] args) {

        //订一杯Espresso，不需要调料
        Beverage beverage = new Espresso();
        System.out.println(beverage.getDescription() + " $" + beverage.cost());

        //来一杯调料为豆浆、摩卡、奶泡的HouseBlend咖啡
        Beverage beverage1 = new HouseBlend();
        beverage1 = new Soy(beverage1);
        beverage1 = new Mocha(beverage1);
        beverage1 = new Whip(beverage1);
        System.out.println(beverage1.getDescription() + " $" + beverage1.cost());
    }
}