Java 装饰者模式

装饰者模式

课题：星巴兹咖啡

beverage：饮料

condiment: 调料

开发-关闭原则：类应该对扩展开放，对修改关闭。

定义装饰者模式

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。

//饮料抽象类
public abstract class Beverage {
  String description = "Unknown Beverage";  
  public String getDescription(){
    return description;
  } 
  public abstract double cost();  
}

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

//具体的饮料类 浓缩咖啡
public class Espresso extends Beverage{
  public Espresso() {
    description = "Espresso";
  } 
  @Override
  public double cost() {
    return 1.99;
  }
}

//具体饮料类
public class HouseBlend extends Beverage{
  public HouseBlend() {
    description = "House Blend Coffee";
  } 
  @Override
  public double cost() {    
    return 0.89;
  }
}

具体调料装饰类
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 0.20 + beverage.cost();
  }
}

public class Whip extends CondimentDecorator{
  Beverage beverage;  
  public Whip(Beverage beverage) {
    this.beverage = beverage;
  } 
  @Override
  public String getDescription() {
    return beverage.getDescription() + " , Whip";
  }
  @Override
  public double cost() {
    return 0.5 + beverage.cost();
  }
}

测试类
public class StarbuzzCoffee {
  public static void main(String[] args) {
    //不需要调料
    Beverage beverage = new Espresso();
    System.out.println(beverage.getDescription()
        + " $" + beverage.cost());
    
    Beverage beverage2 = new HouseBlend();
    beverage2 = new Mocha(beverage2);
    beverage2 = new Whip(beverage2);
    System.out.println(beverage2.getDescription()
        +" $" + beverage2.cost());
  } 
}