装饰者模式

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

饮料抽象类

public abstract class Beverage{

    String description = "";

    public String getDescription(){  return description;}

   public abstract double cost();

}

调料抽象类---装饰者类

public abstract class CondimentDecorator extend Beverage{

    public  abstract String getDescription();

}

浓缩咖啡

public class Espresso extends Beverage(){

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

    public double cost(){  return 1.99;}

}

摩卡咖啡--具体装饰者

public class Mocha extends CondimentDecorator(){  

    Beverage beverage;

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

      public Mocha getDescription(){   return beverage.getDescription() + ",Mocha" ;}  

      public double cost(){    return 0.2 + beverage.cost();}

}

Main

Beverage beverage = new Espresso();

beverage = new Mocha(beverage);//Mocha 装饰

beverage = new Mocha(beverage);//Mocha 装饰

beverage = new Whip(beverage);//Whip 装饰

System.out.print(beverage.getDescription()+" $ " + bevarage.cost())

result:

Espresso Coffee,Mocha,Mocha,Whip $ 3.44

扩展：FilterInputStream  装饰者对象