设计模式（四）--装饰器模式

装饰器模式：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。

意图：将一个接口转换为另一个接口 

设计原则：开闭原则(对类的扩展开放，对修改关闭)

装饰器模式设计要点：

1.装饰者和被装饰对象有相同的超类型

2.可以用一个或者多个装饰者去包装一个对象

3.装饰者可以在所委托被装饰者的行为之前或者之后，加上自己的行为，已达到特定的目的

/**
 * Created by Administrator on 2017/12/10.
 * 饮料类
 */
public abstract class Beverage {
    protected String desc;
    public String getDesc(){
        return desc;
    }
    protected abstract double cost();
}

/**
 * Created by Administrator on 2017/12/10.
 * 调料装饰器
 */
public abstract class CondimentDecorator  extends Beverage{
    public abstract String getDesc();
}

/**
 * Created by Administrator on 2017/12/10.
 *HouseBlend coffee
 */
public class HouseBlend extends Beverage {
    public HouseBlend() {
        desc = "houseBlend";
    }

    @Override
    protected double cost() {
        return 10;
    }
}

/**
 * Created by Administrator on 2017/12/10.
 * 用Mocha去装饰饮料
 */
public class Mocha extends CondimentDecorator {
    private Beverage beverage;

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

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

    @Override
    protected double cost() {
        //可以在这里做一些事情
        double price = 6;
        price = beverage.cost() + price;
        return price;
    }
}

/**
 * Created by Administrator on 2017/12/10.
 */
public class TestDecorator {
    public static void main(String[] args) {
        Beverage beverage = new HouseBlend();
        beverage = new Mocha(beverage); //用mocha去装饰coffee
        System.out.println(beverage.cost() + "," + beverage.getDesc());
        beverage = new Mocha(beverage); //两次用Mocha去装饰coffee
        System.out.println(beverage.cost() + "," + beverage.getDesc());
    }
}