设计模式： 自己手动写一个装饰者模式

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l比继承更有弹性的替代方案。装饰者和被装饰者有相同的超类型，你可以用一个或多个装饰者包装一个对象。既然装饰者和被装饰者有相同的超类型，所以在任何需要原始对象（被装饰者）的场合，可以用装饰过的对象替换它。装饰者可以在所委托被装饰者的行为之前或之后加上自己的行为，已达到特定的目的。对象可以在任何时候被装饰，所以可以在运行时动态地、不限量地用你喜欢的装饰者来装饰对象。

类图：

源代码如下：

package decorator;
/**
 * 饮料的超类
 * @author <span style="font-family: Arial, Helvetica, sans-serif;">Arvon</span>

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

package decorator;
/**
 * 一种饮料 被装饰者
 * @author <span style="font-family: Arial, Helvetica, sans-serif;">Arvon</span><pre name="code" class="java">

* */public class HouseBlend extends Beverage {public HouseBlend() {super();description = "House Blend Coffee";}@Overridepublic float cost() {// TODO Auto-generated method stubreturn 0.89f;}}

package decorator;
/**
 * 佐料装饰类 佐料超类
 * @author Administrator
 *
 */
public abstract class CondimentDecorator extends Beverage {
	public Beverage mBeverage;
	@Override
	public abstract String getDescription();

	@Override
	public abstract float cost();

}

package decorator;
/**
 * 一种佐料 装饰者
 * @author Administrator
 *
 */
public class Milk extends CondimentDecorator {
	
	
	public Milk(Beverage mBeverage) {
		this.mBeverage = mBeverage;
	}

	@Override
	public String getDescription() {
		// TODO Auto-generated method stub
		return "Milk " + mBeverage.getDescription();
	}

	@Override
	public float cost() {
		return .20f + mBeverage.cost();
	}
	
	

}

package decorator;
/**
 * 一种佐料 装饰者
 * @author Administrator
 *
 */
public class Mocha extends CondimentDecorator {
	
	
	public Mocha(Beverage mBeverage) {
		super();
		this.mBeverage = mBeverage;
	}

	@Override
	public String getDescription() {
		// TODO Auto-generated method stub
		return "Mocha "+mBeverage.getDescription();
	}

	@Override
	public float cost() {
		// TODO Auto-generated method stub
		return 1.2f + mBeverage.cost();
	}

}

package decorator;
/**
 * for testing 
 * @author Administrator
 *
 */
public class StarbuzzCoffee {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Beverage mBeverage = new HouseBlend();
		System.out.println(mBeverage.getDescription() 
				+ " $" + mBeverage.cost());
		
		mBeverage = new Milk(mBeverage);
		System.out.println(mBeverage.getDescription() 
				+ " $" + mBeverage.cost());
		mBeverage = new Mocha(mBeverage);
		System.out.println(mBeverage.getDescription() 
				+ " $" + mBeverage.cost());
	}

}

程序的输出: 

House Blend Coffee $0.89
Milk House Blend Coffee $1.09
Mocha Milk House Blend Coffee $2.29