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

本文详细阐述了如何使用装饰者模式为星巴克咖啡连锁店设计饮料菜单,包括不同类型的咖啡和可选调料的组合,展示了如何通过类图和代码实现来满足顾客多样化的口味需求。

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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

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