java-装饰者模式

有一家咖啡店，你想喝杯咖啡，于是你走进咖啡店，咖啡店有主体浓缩咖啡、黑咖啡、深培咖啡，当然，咖啡中也可以加一些调料：豆浆、摩卡、奶泡等。每种咖啡或者调料，价格都不一样，你可以单点一杯咖啡，也可以点一杯咖啡加上自己喜欢的调料。那么价格怎么算呢，我们可以通过装饰者模式试试，先看一下咖啡调料UML类图：

看一下价格计算过程，此图来自《Head First 设计模式》：

再看看java代码：

/**
 * 咖啡抽象类，被装饰者
 */
public abstract class Beverage {
    String description = "咖啡";

    public String getDescription() {
        return description;
    }

    public abstract double cost();
}

/**
 * 调料抽象类,就是装饰者类
 */
public abstract class CondimentDecorator extends Beverage{
    public abstract String getDescription();
}

三种不同的咖啡主体：

/**
 * 浓缩咖啡
 */
public class Espresso extends Beverage {

    public Espresso() {
        description = "浓缩咖啡";
    }

    public double cost() {
        return 1.99;
    }
}

/**
 * 黑咖啡
 */
public class HoseBlend extends Beverage {
    public HoseBlend() {
        description = "黑咖啡";
    }

    public double cost() {
        return 0.99;
    }
}

/**
 * 深焙咖啡
 */
public class DarkRoast extends Beverage {

    public DarkRoast() {
        description = "深焙咖啡";
    }

    public double cost() {
        return 0.19;
    }
}

三种不同的调料：

/**
 * 摩卡
 */
public class Mocha extends CondimentDecorator{
    private Beverage beverage;

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

    public String getDescription() {
        return beverage.getDescription() + ", 摩卡";
    }

    public double cost() {
        return 0.20 + beverage.cost();
    }
}

/**
 * 豆浆
 */
public class Soy extends CondimentDecorator {
    private Beverage beverage;

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

    public String getDescription() {
        return beverage.getDescription() + ", 豆浆";
    }

    public double cost() {
        return 0.23 + beverage.cost();
    }
}

/**
 * 奶泡
 */
public class Whip extends CondimentDecorator {
    private Beverage beverage;

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

    public String getDescription() {
        return beverage.getDescription() + ", 奶泡";
    }

    public double cost() {
        return 0.69 + beverage.cost();
    }
}

最后看一下测试类及结果：

public class StrabuzzCoffee {

    public static void main(String[] args) {
        //单点一杯浓缩咖啡
        Beverage beverage = new Espresso();
        System.out.println(beverage.getDescription() + ", $" + beverage.cost());
        System.out.println("----------------------------------------------");
        //一杯双倍摩卡一份奶泡的黑咖啡
        Beverage beverage2 = new HoseBlend();
        beverage2 = new Mocha(beverage2);
        beverage2 = new Mocha(beverage2);
        beverage2 = new Whip(beverage2);
        System.out.println(beverage2.getDescription() + ", $" + beverage2.cost());
        System.out.println("----------------------------------------------");
        //一杯调料为豆浆、摩卡、奶泡的深焙咖啡
        Beverage beverage3 = new DarkRoast();
        beverage3 = new Soy(beverage3);
        beverage3 = new Mocha(beverage3);
        beverage3 = new Whip(beverage3);
        System.out.println(beverage3.getDescription() + ", $" + beverage3.cost());
        System.out.println("----------------------------------------------");
    }

}

结果：