Java策略模式

Java策略模式

定义了算法家族，分别封装起来，让他们之间可以相互替换，此模式让算法的变化不会影响到使用算法的用户

类型：行为型

使用场景：

系统有很多类，而他们的区别仅仅在于他们的行为不同。

一个系统需要动态地在集中算法中选择一种

优点：

1.开闭原则

2.避免使用多重条件转义语句

3.提高算法的保密性和安全性

缺点：

客户端必须知道所有的策略类，并自行决定使用哪一个策略类

产生了很多策略类

接口：

public interface PromotionsStrategy { void doPromotion();}

执行动作：

private PromotionsStrategy promotionsStrategy; public PromotionActivity(PromotionsStrategy promotionsStrategy) { this.promotionsStrategy = promotionsStrategy; } public void executePromotionsStrategy(){ promotionsStrategy.doPromotion(); }}

为空的情况：

public class EmptyPromotionStrategy implements PromotionsStrategy{ @Override public void doPromotion() { System.out.println("无处销活动"); }}

返现：

public class FanXianPromotionsStrategy implements PromotionsStrategy{ @Override public void doPromotion() { System.out.println("返现促销，返回的金额存放到慕课网用户的余额中"); }}

立减：

public class LiJianPromotionsStrategy implements PromotionsStrategy { @Override public void doPromotion() { System.out.println("立减促销，返回的金额存放到慕课网用户的余额中"); }}

满减：

public class ManJianPromotionsStrategy implements PromotionsStrategy{ @Override public void doPromotion() { System.out.println("满减促销，返回的金额存放到慕课网用户的余额中"); }}

工厂：

import java.util.HashMap;import java.util.Map;public class PromotionsStrategyFactory { private static Map PROMOTION_STRATEGY_MAP = new HashMap(); static { PROMOTION_STRATEGY_MAP.put(PromotionKey.LIJIAN, new LiJianPromotionsStrategy()); PROMOTION_STRATEGY_MAP.put(PromotionKey.FANXIAN, new FanXianPromotionsStrategy()); PROMOTION_STRATEGY_MAP.put(PromotionKey.MANJIAN, new ManJianPromotionsStrategy()); } private static final PromotionsStrategy NON_PROMOTION = new EmptyPromotionStrategy(); private PromotionsStrategyFactory() { } public static PromotionsStrategy getPromotionStrategy(String promotionsKey) { PromotionsStrategy promotionsStrategy = PROMOTION_STRATEGY_MAP.get(promotionsKey); return promotionsStrategy == null ? NON_PROMOTION : promotionsStrategy; } private interface PromotionKey { String LIJIAN = "LIJIAN"; String FANXIAN = "FANXIAN"; String MANJIAN = "MANJIAN"; }}

测试：

public class main { public static void main(String[] args) {// PromotionActivity promotionActivity618=new PromotionActivity(new LiJianPromotionsStrategy());// PromotionActivity promotionActivity1111=new PromotionActivity(new FanXianPromotionsStrategy());//// promotionActivity618.executePromotionsStrategy();// promotionActivity1111.executePromotionsStrategy();// PromotionActivity promotionActivity=null;// String promotionKey="LIJIAN";// if(StringUtils.equals(promotionKey,"LIJIAN")){// promotionActivity=new PromotionActivity(new LiJianPromotionsStrategy());// }else if(StringUtils.equals(promotionKey,"FANXIAN")){// promotionActivity=new PromotionActivity(new FanXianPromotionsStrategy());// }// promotionActivity.executePromotionsStrategy(); String promotionKey="LIJIAN"; PromotionActivity promotionActivity=new PromotionActivity(PromotionsStrategyFactory.getPromotionStrategy(promotionKey)); promotionActivity.executePromotionsStrategy(); }}

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