【设计模式】【策略模式 打折算法】

/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2012, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
public interface DiscountStrategy
{
	//定义一个用于计算打折价的方法
	double getDiscount(double originPrice);
}

/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2012, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
//实现DiscountStrategy接口，实现对VIP打折的算法
public class VipDiscount
	implements DiscountStrategy
{
	//重写getDiscount()方法，提供VIP打折算法
	public double getDiscount(double originPrice)
	{
		System.out.println("使用VIP折扣...");
		return originPrice * 0.5;
	}
}

/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2012, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
public class OldDiscount
	implements DiscountStrategy
{
	//重写getDiscount()方法，提供旧书打折算法
	public double getDiscount(double originPrice)
	{
		System.out.println("使用旧书折扣...");
		return originPrice * 0.7;
	}
}

/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2012, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
public class DiscountContext
{
	//组合一个DiscountStrategy对象
	private DiscountStrategy strategy;
	//构造器，传入一个DiscountStrategy对象
	public DiscountContext(DiscountStrategy strategy)
	{
		this.strategy  = strategy;
	}
	//根据实际所使用的DiscountStrategy对象得到折扣价
	public double getDiscountPrice(double price)
	{
		//如果strategy为null，系统自动选择OldDiscount类
		if (strategy == null)
		{
			strategy = new OldDiscount();
		}
		return this.strategy.getDiscount(price);
	}
	//提供切换算法的方法
	public void changeDiscount(DiscountStrategy strategy)
	{
		this.strategy = strategy;
	}
}

/**
 * Description:
 * <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>
 * <br/>Copyright (C), 2001-2012, Yeeku.H.Lee
 * <br/>This program is protected by copyright laws.
 * <br/>Program Name:
 * <br/>Date:
 * @author  Yeeku.H.Lee kongyeeku@163.com
 * @version  1.0
 */
public class StrategyTest
{
	public static void main(String[] args)
	{
		//客户端没有选择打折策略类
		DiscountContext dc = new DiscountContext(null);
		double price1 = 79;
		//使用默认的打折策略
		System.out.println("79元的书默认打折后的价格是："
			+ dc.getDiscountPrice(price1));
		//客户端选择合适的VIP打折策略
		dc.changeDiscount(new VipDiscount());
		double price2 = 89;
		//使用VIP打折得到打折价格
		System.out.println("89元的书对VIP用户的价格是："
			+ dc.getDiscountPrice(price2));
	}
}