装饰者模式案例

在不必改变原类文件和使用继承的情况下，动态地扩展一个对象的功能。它是通过创建一个包装对象，也就是装饰来包裹真实的对象。
拿一个咖啡对象，以摩卡对象来装饰它，以奶泡对象来装饰它，调用cost方法，并依靠委托将调料的价格加进去
public abstract class Beverage {
     //原味类
     //默认包访问权限
     String description="Unknown Beverage";
     public String getDescription(){
         return description;
     }
     public abstract double cost();
 }

 //调料基础类
 public abstract class CondimentDecorator extends Beverage{
     public abstract String getDescription();
 }

 //一种饮料
 public class Espresso extends Beverage{
     public Espresso(){
         description="Espresso";
     }
     @Override
     public double cost() {
         // TODO Auto-generated method stub
         return 1.99;
     }

 }

 //一种饮料
 public class HouseBlend extends Beverage{
     public HouseBlend(){
         description="House Blend Coffee";
     }
     @Override
     public double cost() {
         // TODO Auto-generated method stub
         return 0.89;
     }

 }

 //一种调料
 public class Mocha extends CondimentDecorator{
     Beverage beverage;
     public Mocha(Beverage beverage){
         this.beverage=beverage;
     }
     @Override
     public String getDescription() {
         // TODO Auto-generated method stub
         return beverage.getDescription()+",Mocha";
     }

     @Override
     public double cost() {
         // TODO Auto-generated method stub
         return 0.20+beverage.cost();
     }

 }

 public class Soy extends CondimentDecorator{
     Beverage beverage;
     public Soy(Beverage beverage){
         this.beverage=beverage;
     }
     @Override
     public String getDescription() {
         // TODO Auto-generated method stub
         return beverage.getDescription()+",Soy";
     }

     @Override
     public double cost() {
         // TODO Auto-generated method stub
         return 0.20+beverage.cost();
     }

 }
public class Whip extends CondimentDecorator{
     Beverage beverage;
     public Whip(Beverage beverage){
         this.beverage=beverage;
     }
     @Override
     public String getDescription() {
         // TODO Auto-generated method stub
         return beverage.getDescription()+",Whip";
     }

     @Override
     public double cost() {
         // TODO Auto-generated method stub
         return 0.20+beverage.cost();
     }

 }

 测试：public class MyTest {

     public static void main(String[] args) {
         // TODO Auto-generated method stub
         Beverage beverage=new Espresso();//订了一杯Espresso，不需要调料，打印出它的描述与价格
         System.out.println(beverage.getDescription()+" $"+beverage.cost());
         Beverage beverage2=new Espresso();
         beverage2=new Mocha(beverage2);
         beverage2=new Mocha(beverage2);
         beverage2=new Whip(beverage2);
         System.out.println(beverage2.getDescription()+" $"+beverage2.cost());
         
         Beverage beverage3=new HouseBlend();
         beverage3=new Soy(beverage3);
         beverage3=new Mocha(beverage3);
         beverage3=new Whip(beverage3);
         System.out.println(beverage3.getDescription()+" $"+beverage3.cost());
     }

 }效果：
Espresso $1.99
 Espresso,Mocha,Mocha,Whip $2.5900000000000003
 House Blend Coffee,Soy,Mocha,Whip $1.49