设计模式之三：装饰者模式(简单实现(星巴兹咖啡))

 装饰者模式：动态地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。(星巴兹咖啡)

设计原则：类应该对扩展开放，对修改关闭。

我们的目标是允许类容易扩展，在不修改现有代码的情况下，就可以搭配新的行为。如能实现这样的目标，有什么好处呢？这样的设计具有弹性可以应对改变，可以接受新的功能来应对改变的需求。

工程名称：Decorator(eclipse)  下载目录：http://www.cnblogs.com/jrsmith/admin/Files.aspx ，Decorator.zip

package com.jyu.abstractclass;

/**
 * 饮料(组件)
 * @author JRSmith
 *
 */
public abstract class Beverage {

    protected String description = "Unknown Beverage";
    
    /**getDescription()已经在此实现了，但是cost()必须在子类中实现*/
    public String getDescription(){
        return description;
    }
    
    public abstract double cost();
}

package com.jyu.abstractclass;

/**
 * 调料
 * @author JRSmith
 *
 */
public abstract class Condiment extends Beverage {

    @Override
    public abstract String getDescription();
}

package com.jyu.extendsbeverage;

import com.jyu.abstractclass.Beverage;

/**
 * 低咖啡因
 * @author JRSmith
 *
 */
public class Decat extends Beverage {

    public Decat() {
        description = "Decat Coffee";
    }

    @Override
    public double cost() {
        return 1.05;
    }

}

package com.jyu.extendsbeverage;

import com.jyu.abstractclass.Beverage;

/**
 * 深焙
 * @author JRSmith
 *
 */
public class DarkRoast extends Beverage {

    public DarkRoast() {
        description = "DarkRoast Coffee";
    }

    @Override
    public double cost() {
        return .99;
    }

}

package com.jyu.extendsbeverage;

import com.jyu.abstractclass.Beverage;

/**
 * 浓缩咖啡
 * @author JRSmith
 *
 */
public class Espresso extends Beverage {

    public Espresso(){
        description = "Espresso Coffee";
    }
    
    @Override
    public double cost() {
        return 1.99;
    }

}

package com.jyu.extendsbeverage;

import com.jyu.abstractclass.Beverage;

/**
 * 综合咖啡
 * @author JRSmith
 *
 */
public class HouseBlend extends Beverage {

    public HouseBlend() {
        description = "House Blend Coffee";
    }

    @Override
    public double cost() {
        return .89;
    }

}

package com.jyu.extendscondiment;

import com.jyu.abstractclass.Beverage;
import com.jyu.abstractclass.Condiment;

/**
 * 摩卡
 * @author JRSmith
 *
 */
public class Mocha extends Condiment {

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

    @Override
    public String getDescription() {
        return this.beverage.getDescription() + " , Mocha";
    }

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

}

package com.jyu.extendscondiment;

import com.jyu.abstractclass.Beverage;
import com.jyu.abstractclass.Condiment;

/**
 * 豆浆
 * @author JRSmith
 *
 */
public class Soy extends Condiment {

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

    @Override
    public String getDescription() {
        return this.beverage.getDescription() + " , Soy";
    }

    @Override
    public double cost() {
        return 0.15 + this.beverage.cost();
    }

}

package com.jyu.extendscondiment;

import com.jyu.abstractclass.Beverage;
import com.jyu.abstractclass.Condiment;

/**
 * 奶泡
 * @author JRSmith
 *
 */
public class Whip extends Condiment {

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

    @Override
    public String getDescription() {
        return this.beverage.getDescription() + " , Whip";
    }

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

}

package com.jyu.test;

import com.jyu.abstractclass.Beverage;
import com.jyu.extendsbeverage.DarkRoast;
import com.jyu.extendsbeverage.Espresso;
import com.jyu.extendsbeverage.HouseBlend;
import com.jyu.extendscondiment.Mocha;
import com.jyu.extendscondiment.Soy;
import com.jyu.extendscondiment.Whip;

public class StarbuzzCoffee {

    /**
     * @param args
     */
    public static void main(String[] args) {
        
        /**订一杯Espresso，不需要调料，打印出它的描述与价钱*/
        Beverage beverage = new Espresso();
        System.out.println(beverage.getDescription() + " $" + beverage.cost());
        
        /**制造出一个DarkRoast对象。用Mocha装饰它，用第二个Mocha装饰它，用Whip装饰它*/
        Beverage beverage2 = new DarkRoast();
        beverage2 = new Mocha(beverage2);
        beverage2 = new Mocha(beverage2);
        System.out.println(beverage2.getDescription() + " $" + beverage2.cost());
        
        /**最后，再来一杯调料为豆浆、摩卡、奶泡的HouseBlend咖啡*/
        Beverage beverage3 = new HouseBlend();
        beverage3 = new Soy(beverage3);
        beverage3 = new Mocha(beverage3);
        beverage3 = new Whip(beverage3);
        System.out.println(beverage3.getDescription() + " $" + beverage3.cost());
        
        
    }

}