装饰者模式(Decorator Pattern)（二）：HeadFirst中咖啡添加调料

一、问题描述

为星巴兹咖啡连锁店设计饮料菜单，咖啡可加的调料有豆浆、牛奶、摩卡等。可在咖啡的基础上加入不同的调料，星巴兹会根据所加的调料收取不同的费用，要注意到，以后可能有新的调料被加入进来供顾客选择。并且本店现有DarkRoast（深焙）、HouseBlend（综合）、Decaf（低咖啡因）及Espresso（浓咖啡）四种类型的咖啡，而且以后可能会添加新的咖啡种类。

使用装饰者模式，四种咖啡为具体组件，调料为具体装饰者。

二、类图

三、代码实现

1.抽象组件角色：Beverage（饮料）

public abstract class Beverage {
	String description = "Unknown Beverage";
  
	public String getDescription() {
		return description;
	}
	public abstract double cost();
}

2.具体组件角色：四种类型的咖啡

(1)DarkRoast

public class DarkRoast extends Beverage {
	public DarkRoast() {
		description = "Dark Roast Coffee";
	}
 
	public double cost() {
		return .99;
	}
}

(2)Decaf

public class Decaf extends Beverage {
	public Decaf() {
		description = "Decaf Coffee";
	}
 
	public double cost() {
		return 1.05;
	}
}

(3)Espresso

public class Espresso extends Beverage {
  
	public Espresso() {
		description = "Espresso";
	}
  
	public double cost() {
		return 1.99;
	}
}

(4)HouseBlend

public class HouseBlend extends Beverage {
	public HouseBlend() {
		description = "House Blend Coffee";
	}
 
	public double cost() {
		return .89;
	}
}

3.装饰者角色：CondimentDecorator

public abstract class CondimentDecorator extends Beverage {
	public abstract String getDescription();
}

4.具体装饰者：各种调料

(1)Milk

public class Milk extends CondimentDecorator {
	Beverage beverage;

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

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

	public double cost() {
		return .10 + beverage.cost();
	}
}

(2)Mocha

public class Mocha extends CondimentDecorator {
	Beverage beverage;
 
	public Mocha(Beverage beverage) {
		this.beverage = beverage;
	}
 
	public String getDescription() {
		return beverage.getDescription() + ", Mocha";
	}
 
	public double cost() {
		return .20 + beverage.cost();
	}
}

(3)Whip

public class Whip extends CondimentDecorator {
	Beverage beverage;
 
	public Whip(Beverage beverage) {
		this.beverage = beverage;
	}
 
	public String getDescription() {
		return beverage.getDescription() + ", Whip";
	}
 
	public double cost() {
		return .10 + beverage.cost();
	}
}

(4)Soy

public class Soy extends CondimentDecorator {
	Beverage beverage;

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

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

	public double cost() {
		return .15 + beverage.cost();
	}
}

5.测试

public class StarbuzzCoffee
{

	public static void main(String args[])
	{
		Beverage beverage = new Espresso();
		System.out.println(beverage.getDescription() + " $" + beverage.cost());

		Beverage beverage2 = new DarkRoast();
		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());
	}
}

四、其他

对于抽象构件角色是由抽象类还是接口实现，以及是否需要实现装饰者角色等，这要根据具体的需要选择。变化的需求促使我们不断对系统进行更改和优化。

转载请注明出处：http://blog.youkuaiyun.com/jialinqiang/article/details/8882993