Java设计模式（三） 装饰模式

装饰模式：动态的将责任附加到对象上，想要扩展功能，装饰者提供有别于继承的另一种选择。

1，创建顶级类

package com.pattern.decorate;

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

2，创建产品类

package com.pattern.decorate;

public class Espresso extends Beverage{
	
	public Espresso(){
		description = "Espresso";
	}
	/** 
	 * @see com.pattern.decorate.Beverage#cost()
	 */
	@Override
	public double cost() {
		return 1.99;
	}
}

package com.pattern.decorate;

public class HouseBlend extends Beverage{

	public HouseBlend(){
		description = "House Blend Coffee";
	}
	
	/** 
	 * @see com.pattern.decorate.Beverage#cost()
	 */
	@Override
	public double cost() {
		return .89;
	}

}

package com.pattern.decorate;

public class DarkRoast extends Beverage {

	public DarkRoast(){
		description = "DarkRoast";
	}
	/** 
	 * @see com.pattern.decorate.Beverage#cost()
	 */
	@Override
	public double cost() {
		return 2.99;
	}

}

3，创建装饰类

package com.pattern.decorate;

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

4，创建装饰类的具体实现类

package com.pattern.decorate;

public  class Whip extends CondimentDecorator {
	
	public Beverage beverage;

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

	/** 
	 * @see com.pattern.decorate.CondimentDecorator#getDescription()
	 */
	@Override
	public String getDescription() {
		return beverage.getDescription()+", Whip";
	}

	/** 
	 * @see com.pattern.decorate.Beverage#cost()
	 */
	@Override
	public double cost() {
		return .30+beverage.cost();
	}

}

package com.pattern.decorate;

public class Mocha extends CondimentDecorator{

	Beverage beverage;
	
	public Mocha(Beverage beverage){
		this.beverage = beverage;
	}
	
	/** 
	 * @see com.pattern.decorate.CondimentDecorator#getDescription()
	 */
	@Override
	public String getDescription() {
		return beverage.getDescription()+", Mocha";
	}

	/** 
	 * @see com.pattern.decorate.Beverage#cost()
	 */
	@Override
	public double cost() {
		return .20+beverage.cost();
	}

}

5，测试

package com.pattern.decorate;

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());
	}
}

上图装饰类与被装饰类 具有共同的父类。

其实也可以不具有相同的父类！