学习笔记之装饰者模式

装饰者（Decorator）模式又名包装（Wrapper）模式，它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。
[code]
package org.kangsg219.abst;

//星巴兹咖啡抽象类
public abstract class Beverage {

public String description="Unknown Beverage!";

public String getDescription(){
return description;
}

public abstract double cost();

}

[/code]
[code]
package org.kangsg219.abst;

//调料(Condiment)抽象类
public abstract class CondimentDecorator extends Beverage {
public abstract String getDescription();

}

[/code]
[code]
package org.kangsg219.impl;

import org.kangsg219.abst.Beverage;

//浓缩咖啡(Espresso)具体类
public class Espresso extends Beverage {

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

@Override
public double cost() {

return 1.99;
}

}

[/code]
[code]
package org.kangsg219.impl;

import org.kangsg219.abst.Beverage;
//HouseBlend咖啡具体类
public class HouseBlend extends Beverage {

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

@Override
public double cost() {

return 0.89;
}

}

[/code]
[code]
package org.kangsg219.impl;

import org.kangsg219.abst.Beverage;
import org.kangsg219.abst.CondimentDecorator;

public class Mocha extends CondimentDecorator {

public Beverage beverage;

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

@Override
public String getDescription() {

return beverage.getDescription()+",mocha";
}

@Override
public double cost() {

return beverage.cost()+0.20;
}

}

[/code]
[code]
package org.kangsg219.impl;

import org.kangsg219.abst.Beverage;
import org.kangsg219.abst.CondimentDecorator;

//奶泡具体装饰类
public class Whip extends CondimentDecorator {

public Beverage beverage;

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

@Override
public String getDescription() {

return beverage.getDescription()+",Whip";
}

@Override
public double cost() {

return beverage.cost()+ 0.10;
}

}

[/code]
[code]
package org.kangsg219.test;

import org.kangsg219.abst.Beverage;
import org.kangsg219.impl.Espresso;
import org.kangsg219.impl.HouseBlend;
import org.kangsg219.impl.Mocha;
import org.kangsg219.impl.Whip;

public class StarbuzzCoffee {


public static void main(String[] args) {
//仅要一杯浓缩咖啡，不要调料。
Beverage beverage=new Espresso();
System.out.println(beverage.getDescription()+" $"+beverage.cost());

//双倍摩卡的HouseBlend咖啡
Beverage beverage2=new HouseBlend();
beverage2=new Mocha(beverage2);
beverage2=new Mocha(beverage2);
beverage2=new Whip(beverage2);
System.out.println(beverage2.getDescription()+" $"+beverage2.cost());
}

}

[/code]
运行结果：
Espresso $1.99
HouseBlend,mocha,mocha,Whip $1.39