简介

策略模式，定义了一个算法族，并且封装了每一个算法，使它们可以互相替换。策略模式让算法与使用它的客户端独立的变化。

UML 类图

示例

策略模式比较常见。人总要学习，正如在开篇中所说，通过读可以，写效果更好，能够通过分享或者教会别人可能会更有效。
策略相关类，strategy.h

#ifndef STRATEGY_H
#define STRATEGY_H
#include <iostream>

using namespace std;
class CLearning
{
public:
    virtual void Learn() = 0;};

class CReading:public CLearning
{
public:
    void Learn()
    {cout<<"Learn by Reading."<<endl;}
};

class CWriting:public CLearning
{void Learn()
    {cout<<"Learn by Writing."<<endl;}
};

class CTeaching:public CLearning
{void Learn()
    {cout<<"Learn by Teaching."<<endl;}
};

class CLearningContext
{
public:
    CLearningContext(CLearning* pLearning)
    {m_pLearning = pLearning;}
    void Learn()
    {m_pLearning->Learn();
    }
private:
    CLearning* m_pLearning;
};
#endif

客户端调用，main.cpp

#include "strategy.h"

#define SAFE_DELETE(p) if(p){delete (p); (p) = NULL;}
int main(int argc, char* argv[])
{
    CWriting* pWriting = new CWriting;
    CLearningContext* pContext = new CLearningContext(pWriting);
    pContext->Learn();
    SAFE_DELETE(pWriting);
    SAFE_DELETE(pContext);
    return 0;
}

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。
类型 ： 行为型
适用场景：

• 系统有很多类，而它们的区别仅仅在于它们的行为不同
• 一个系统需要动态地在几种算法中选择一种

优点：

• 开闭原则
• 避免使用多重条件转移语句（if…else…,switch）
• 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。
• 产生很多策略类

案例

某知识平台的教学视频促销（满减、立减、返现）

促销策略接口

public interface PromotionStrategy {void doPromotion();
}

返现策略

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");
    }
}

立减策略

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");
    }
}

满减策略

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

促销活动

public class PromotionActivity {
    private PromotionStrategy promotionStrategy;

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

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

}

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

        promotionActivity618.executePromotionStrategy();
        promotionActivity1111.executePromotionStrategy();}
}

结果：