装饰者模式——Java设计模式

装饰模式

1.概念

动态地为对象附加上额外的职责
其目的是包装一个对象，从而可以在运行时动态添加新的职责。每个装饰器都可以包装另一个装饰器，这样理论上来说可以对目标对象进行无限次的装饰。

2.装饰器类图

3.代码

一个早餐店经营两种主食：汉堡和吐司，一段时间后需要加个配料。
主要思路是：以主食（汉堡、吐司）为主体，然后再运行时以配料（火腿、起司）装饰为主食。其UML图为：

(1)抽象构建类————Breakfast.java，早餐的抽象父类

public abstract class Breakfast {
    public String description="未知";
    public String getDescription(){
        return description;
    }
    public abstract Double cost();
}

(2)抽象装饰类————CondimentDecorator.java，是早餐抽象类的子类

public abstract class CondimentDecorator extends Breakfast{
    Breakfast myfood;
    public CondimentDecorator(Breakfast myfood){
        this.myfood=myfood;
    }
    @Override
    public String getDescription(){
        return myfood.getDescription();
    }
    @Override
    public Double cost(){
        return myfood.cost();
    }
}

(3)具体构建类————Toast.java、Burger.java
Toast.java

public class Toast extends Breakfast {
    public Toast(){
        description="吐司";
    }
    public Double cost(){
        return 10d;
    }
}

Burger.java

public class Burger extends Breakfast {
    public Burger(){
        description="汉堡";
    }
    @Override
    public Double cost(){
        return 15d;
    }
}

(4)具体装饰类————Cheese.java、Ham.java
Cheese.java

public class Cheese extends CondimentDecorator {
    public Cheese(Breakfast myfood) {
        super(myfood);
    }

    @Override
    public Double cost() {
        return super.cost() + 5;
    }

    @Override
    public String getDescription() {
        return super.getDescription() + ",起司";
    }
}

Ham.java

public class Ham extends CondimentDecorator {
    public Ham(Breakfast myfood) {
        super(myfood);
    }

    @Override
    public Double cost() {
        return super.cost() + 10;
    }

    @Override
    public String getDescription() {
        return super.getDescription() + ",火腿";
    }
}

(5)客户端测试类

public class Decorator {
    public static void main(String args[]) {
        Breakfast breakfast1 = new Toast();
        System.out.println("您点的餐点为：" + breakfast1.getDescription() + "。价格为：" + breakfast1.cost());
        Breakfast breakfast2 = new Toast();
        breakfast2 = new Ham(breakfast2);
        breakfast2 = new Ham(breakfast2);
        System.out.println("您点的餐点为：" + breakfast2.getDescription() + "。价格为：" + breakfast2.cost());
        Breakfast breakfast3 = new Burger();
        breakfast3 = new Ham(breakfast3);
        breakfast3 = new Cheese(breakfast3);
        breakfast3 = new Cheese(breakfast3);
        System.out.println("您点的餐点为：" + breakfast3.getDescription() + "。价格为：" + breakfast3.cost());
    }
}

结果

您点的餐点为：吐司。价格为：10.0
您点的餐点为：吐司,火腿,火腿。价格为：30.0
您点的餐点为：汉堡,火腿,起司,起司。价格为：35.0

详细见：Java设计模式