一、要完成的任务
星巴兹(Starbuzz)是以扩张速度最快而闻名的咖啡连锁店。如果你在街角看到它的店,在对面街上肯定还会看到另一家。因为扩张速度实在太快了,他们准备更新订单系统,以合乎他们的饮料供应要求。他们原先的类设计是这样的..
购买咖啡时,也可以要求在其中加入各种调料,例如:蒸奶(Steamed Milk)、豆浆(Soy)、摩卡(Mocha,也就是巧克力风味)或覆盖奶泡。星巴兹会根据所加入的调料收取不同的费用。所以订单系统必须考虑到这些调料部分。
二、Decorator模式
1、一个原则
类应该对扩展开放,对修改关闭
2、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。
3.分析任务
4.设计任务
三、代码实现
1.定义抽象类
(1)饮料抽象类Beverage
Beverage.java package com.sterning.ch3_decorator;
/**//* * Beverage是一个抽象类,有两个方法 */ public abstract class Beverage { public String description="Unknown Beverage"; /**//* * getDescription()已经在此实现了,但是cost()必须在子类中实现 */ public String getDescription() { return description; } public abstract double cost(); }
(2)调料抽象类CondimentDecorator
CondimentDecorator.java package com.sterning.ch3_decorator;
/**//* * 首先,必须让CondimentDecorator能够取代Beverage,所以将CondimentDecorator扩展自Beverage类 */ public abstract class CondimentDecorator extends Beverage {
//所有的调料装饰者都必须重新实现getDescription()方法. public abstract String getDescription(); }
2.饮料实现
(1)Espresso
Espresso.java package com.sterning.ch3_decorator;
/**//* * 首先,必须让CondimentDecorator能够取代Beverage,所以将CondimentDecorator扩展自Beverage类 */ public abstract class CondimentDecorator extends Beverage {
//所有的调料装饰者都必须重新实现getDescription()方法. public abstract String getDescription(); }
(2)HouseBlend
HouseBlend.java package com.sterning.ch3_decorator.drink;
import com.sterning.ch3_decorator.Beverage;
public class HouseBlend extends Beverage { public HouseBlend() { description="House Blend Coffee"; }
@Override public double cost() { return 0.89; }
}
(3)DarkRoast
DarkRoast.java package com.sterning.ch3_decorator.drink;
import com.sterning.ch3_decorator.Beverage;
public class DarkRoast extends Beverage { public DarkRoast() { description="Dark Roast Coffee"; }
@Override public double cost() { return 0.99; } }
(4)Decaf
Decaf.java package com.sterning.ch3_decorator.drink;
import com.sterning.ch3_decorator.Beverage;
public class Decaf extends Beverage { public Decaf() { description="Decaf Coffee"; }
@Override public double cost() { return 1.05; } }
3.调料实现
(1)Mocha
Mocha.java package com.sterning.ch3_decorator.condiment;
import com.sterning.ch3_decorator.Beverage; import com.sterning.ch3_decorator.CondimentDecorator;
public class Mocha extends CondimentDecorator { /**//* * 要让Mocha能够引用一个Beverage,做法如下:一是用一个实例变量记录饮料,也就是被装饰者. * 二是想办法让装饰者(饮料)记录到实例变量中,即把饮料当作构造器的参数,再由构造器将此饮料记录在实例变量中 */ Beverage beverage;
public Mocha(Beverage beverage) { this.beverage = beverage; }
@Override public String getDescription() { /**//* * 我们希望叙述不只是描述饮料,而是完整的连调料都描述出来 */ return beverage.getDescription()+",Mocha"; } @Override public double cost() { /**//* * 要计算带Mocha饮料的价钱,首先把调用委托给装饰对象,以计算价钱,然后再加上Mocha的价钱,得到最后结果 */ return 0.20+beverage.cost(); } }
(2)Soy
Soy.java package com.sterning.ch3_decorator.condiment;
import com.sterning.ch3_decorator.Beverage; import com.sterning.ch3_decorator.CondimentDecorator;
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(); } }
(3)Whip
Whip.java package com.sterning.ch3_decorator.condiment;
import com.sterning.ch3_decorator.Beverage; import com.sterning.ch3_decorator.CondimentDecorator; 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.测试类StarbuzzCoffee
StarbuzzCoffee.java package com.sterning.ch3_decorator;
import com.sterning.ch3_decorator.condiment.Mocha; import com.sterning.ch3_decorator.condiment.Soy; import com.sterning.ch3_decorator.condiment.Whip; import com.sterning.ch3_decorator.drink.DarkRoast; import com.sterning.ch3_decorator.drink.Espresso; import com.sterning.ch3_decorator.drink.HouseBlend;
public class StarbuzzCoffee { public static void main(String args[]){ /**//* * 订一杯Espresso,不需要调料,打印出它的描述和价钱. */ Beverage beverage=new Espresso(); System.out.println(beverage.getDescription()+" $"+beverage.cost()); /**//* * 制造一个DarkRoast对象,用Mocha,Whip装饰它 */ Beverage beverage2=new DarkRoast(); beverage2=new Mocha(beverage2); beverage2=new Mocha(beverage2); beverage2=new Whip(beverage2); System.out.println(beverage2.getDescription()+" $"+beverage2.cost()); /**//* * 最后,再来一杯调料为豆浆,摩卡\奶泡的HouseBlend咖啡 */ Beverage beverage3=new HouseBlend(); beverage3=new Soy(beverage3); beverage3=new Mocha(beverage3); beverage3=new Whip(beverage3); System.out.println(beverage3.getDescription()+" $"+beverage3.cost()); } }
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