JAVA设计模式---装饰者模式

写在前面的话：

　　该模式动态的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。装饰者可以在被装饰者的行为前面与/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。

　　该模式的实现意味着一群装饰者类，这些类反映出被装饰的组件类型，用来包装具体组件。

缺点在于，可以用无数个装饰者包装一个组件，但会导致设计中出现许多小对象，如果过度引用，会让程序变得很复杂。

案例分析：

需求：模拟 StarbuzzCoffee 的订单系统，咖啡原种类为Espresso,HouseBlend，添加调料种类分别为Soy,Mocha,Whip,对应不同的收费，杯子分为大中小三种，分别对应不同的收费

代码实现：

1）咖啡部分：

public abstract class Beverage {
    String description = "Unknown Beverage";

    public String getDescription(){
        return description;
    }

    public abstract double cost();
}
public class Espresso extends Beverage {
    public Espresso() {
        description = "Espresso";
    }

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

public class HouseBlend extends Beverage {
    public HouseBlend() {
        description = "HouseBlend";
    }

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

2）调料部分：

public abstract class CondimentBeverage extends Beverage {
    public abstract String getDescription();
}

public class Soy extends CondimentBeverage {
    Beverage beverage;

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

    @Override
    public String getDescription() {
        return beverage.getDescription();
    }

    @Override
    public double cost() {
        return 0.30+beverage.cost();
    }
}

public class Mocha extends CondimentBeverage {
    Beverage beverage;

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

    @Override
    public String getDescription() {
        return beverage.getDescription();
    }

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

public class Whip extends CondimentBeverage {
    Beverage beverage;

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

    @Override
    public String getDescription() {
        return beverage.getDescription();
    }

    @Override
    public double cost() {
        return 0.40+beverage.cost();
    }
}

　3) 杯子选择：

public abstract class Size extends Beverage {
    public abstract String getDescription();
}

public class BigSize extends Size {
    Beverage beverage;

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

    @Override
    public String getDescription() {
        return beverage.getDescription();
    }

    @Override
    public double cost() {
        return 0.30+beverage.cost();
    }
}

public class MiddleSize extends Size {
    Beverage beverage;

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

    @Override
    public String getDescription() {
        return beverage.getDescription();
    }

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

public class SmalleSize extends Size {
    Beverage beverage;

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

    @Override
    public String getDescription() {
        return beverage.getDescription();
    }

    @Override
    public double cost() {
        return 0.10+beverage.cost();
    }
}

　4）测试代码---生产订单：

public class StarbuzzCoffee {
    public static void main(String[] args) {
        Beverage beverage1 = new Espresso();   //订一杯Espresso，不添加任何调料
        System.out.println(beverage1.getDescription()+":$"+beverage1.cost());

        Beverage beverage2 = new HouseBlend();   //订一杯HouseBlend，不添加任何调料
        beverage2 = new Mocha(beverage2);
        beverage2 = new Mocha(beverage2);   //两份摩卡
        System.out.println(beverage2.getDescription()+"(double Mocha):$"+beverage2.cost());

        beverage2 = new Soy(beverage2);     //再加一份soy
        System.out.println(beverage2.getDescription()+"(additional Soy):$"+beverage2.cost());

        beverage2 = new Whip(beverage2);     //再加一份whip
        System.out.println(beverage2.getDescription()+"(additional Whip):$"+beverage2.cost());

        beverage2 = new MiddleSize(beverage2);   //选择中杯
        System.out.println(beverage2.getDescription()+"(choose middleSize):$"+beverage2.cost());
    }
}

　测试结果：

Espresso:$1.99
HouseBlend(double Mocha):$1.29
HouseBlend(additional Soy):$1.59
HouseBlend(additional Whip):$1.99
HouseBlend(choose middleSize):$2.19