策略模式

1.定义：定义了算法家族，分别封装起来，让它们之间可以互相替换，
　　　   此模式让算法的变化不会影响到使用算法的用户。

2.类型：行为型

3.适用场景：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几种算法中选择一种。

4.优点：符合开闭原则；避免使用多重条件转移语句；提高算法的保密性和安全性。

5.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；产生很多策略类。

6.相关设计模式：工厂模式、状态模式。

7.实例目录package

8.实例UML类图

9.代码

package com.geely.design.pattern.behavioral.strategy;

public interface PromotionStrategy {
    void doPromotion();
}

package com.geely.design.pattern.behavioral.strategy;

public class LiJianPromotionStrategy implements PromotionStrategy {
    @Override
    public void doPromotion() {
        System.out.println("立减促销，课程的价格直接减去配置的价格");
    }
}

package com.geely.design.pattern.behavioral.strategy;

public class ManJianPromotionStrategy implements PromotionStrategy {
    @Override
    public void doPromotion() {
        System.out.println("满减促销，满200-20元");
    }
}

package com.geely.design.pattern.behavioral.strategy;

public class FanXianPromotionStrategy implements PromotionStrategy{
    @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");
    }
}

package com.geely.design.pattern.behavioral.strategy;

public class EmptyPromotionStrategy implements PromotionStrategy{
    @Override
    public void doPromotion() {
        System.out.println("无促销活动");
    }
}

package com.geely.design.pattern.behavioral.strategy;

import java.util.HashMap;
import java.util.Map;

public class PromotionStrategyFactory {
    private static final PromotionStrategy NON_PROMOTION = new EmptyPromotionStrategy();
    private static Map<String,PromotionStrategy> PROMOTION_STRATEGY_MAP = new HashMap<>();
    static{
        PROMOTION_STRATEGY_MAP.put(PromotionKey.LIJIAN,new LiJianPromotionStrategy());
        PROMOTION_STRATEGY_MAP.put(PromotionKey.MANJIAN,new ManJianPromotionStrategy());
        PROMOTION_STRATEGY_MAP.put(PromotionKey.FANXIAN,new FanXianPromotionStrategy());
    }

    private PromotionStrategyFactory(){
    }
    public static PromotionStrategy getPromotionStrategy(String promotionKey){
        PromotionStrategy promotionStrategy =PROMOTION_STRATEGY_MAP.get(promotionKey);
        return promotionStrategy == null ? NON_PROMOTION : promotionStrategy;
    }

    private interface PromotionKey{
        String LIJIAN = "LIJIAN";
        String FANXIAN = "FANXIAN";
        String MANJIAN = "MANJIAN";
    }
}

package com.geely.design.pattern.behavioral.strategy;

public class PromotionActivity {
    private PromotionStrategy promotionStrategy;

    public PromotionActivity(PromotionStrategy promotionStrategy){
        this.promotionStrategy = promotionStrategy;
    }

    public void executePromotionStategy(){
        promotionStrategy.doPromotion();
    }
}

package com.geely.design.pattern.behavioral.strategy;

import org.apache.commons.lang.StringUtils;

public class Test {
    /*public static void main(String[] args) {
        PromotionActivity promotionActivity618 = new PromotionActivity(new LiJianPromotionStrategy());
        PromotionActivity promotionActivity1111 = new PromotionActivity(new FanXianPromotionStrategy());
        PromotionActivity promotionActivity1212 = new PromotionActivity(new ManJianPromotionStrategy());

        promotionActivity618.executePromotionStategy();
        promotionActivity1111.executePromotionStategy();
        promotionActivity1212.executePromotionStategy();
    }*/

    /*public static void main(String[] args) {
        PromotionActivity promotionActivity = null;
        String promotionKey = "LIJIAN";
        if(StringUtils.equals(promotionKey,"LIJIAN")){
            promotionActivity = new PromotionActivity(new LiJianPromotionStrategy());
        }else if(StringUtils.equals(promotionKey,"MANJIAN")){
            promotionActivity = new PromotionActivity(new ManJianPromotionStrategy());
        }else if(StringUtils.equals(promotionKey,"FANXIAN")){
            promotionActivity = new PromotionActivity(new FanXianPromotionStrategy());
        }
        promotionActivity.executePromotionStategy();
    }*/

    public static void main(String[] args) {
        String promotionKey = "LIJIAN";
        PromotionActivity promotionActivity =
                new PromotionActivity(PromotionStrategyFactory.getPromotionStrategy(promotionKey));
        promotionActivity.executePromotionStategy();
    }
}