装饰者模式

Demo场景：对不同类型的coffee进行计价。
被装饰对象可以被多个装饰者装饰；理解java.io.*中类之间的关系。

（1）装饰者与被装饰者共同抽象基类：Beverage

package designpattern.decorator.coffee;

/**
 * 装饰者和装饰对象共同的基类
 */
public abstract class Beverage {

    String description = "Unknow Beverage";

    public String getDescription(){
        return description;
    }

    public abstract double cost();
}

（2）被装饰对象：Espresso

package designpattern.decorator.coffee;

public class Espresso extends Beverage {

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

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

}

（3）装饰者抽象类：CondimentDecorator

package designpattern.decorator.coffee;

/**
 *  需要让装饰者类能够取代基类（Beverage），所以要集成基类
 */
public abstract class CondimentDecorator extends Beverage {

    public abstract String getDescription();

}

（4）装饰者继承类：Mocha

package designpattern.decorator.coffee;

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 beverage.cost() + 0.2;
    }

}

装饰者模型演示：

package designpattern.decorator.coffee;

public class StarbuzzCoffee {

    public static void main(String[] args) {
        Beverage beverage = new Espresso();
        //不加装饰者类，直接输出
        System.out.println(beverage.getDescription() + " $" + beverage.cost());

        //添加装饰者类，再输出
        beverage = new Mocha(beverage); 
        System.out.println(beverage.getDescription() + " $" + beverage.cost());
    }

}