《大话设计模式》读书笔记（C++代码实现） 第二章：策略模式

　　

　　策略模式（Strategy）：它定义了算法家庭，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客户。

1.策略模式说明：

　　

// StrategyTest01.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
using namespace std;

//定义所有支持算法的公用接口
//抽象算法类
class Strategy
{
public :
    virtual void AlgorithmInterface() = 0;
};

class ConcreteStrategyA : public Strategy
{
public :
    void AlgorithmInterface()
    {
        cout<<"算法A实现"<<endl;
    }
};

class ConcreteStrategyB : public Strategy
{
public :
    void AlgorithmInterface()
    {
        cout<<"算法B实现"<<endl;
    }
};

class ConcreteStrategyC : public Strategy
{
public :
    void AlgorithmInterface()
    {
        cout<<"算法C实现"<<endl;
    }
};


class Context 
{
private :
    Strategy* strategy;

public :
    //初始化时，传入具体的策略对象
    Context(Strategy* strategy)
    {
        this->strategy = strategy;
    }
    //上下文接口
    //根据具体的策略对象，调用其算法的方法
    void ContextInterface()
    {
        this->strategy->AlgorithmInterface();
    }
};


int _tmain(int argc, _TCHAR* argv[])
{
    ConcreteStrategyA a;
    ConcreteStrategyB b;
    ConcreteStrategyC c;

    Context c1(&a);
    c1.ContextInterface();

    Context c2(&b);
    c2.ContextInterface();

    Context c3(&c);
    c3.ContextInterface();

    system("pause");
    return 0;
}

 2.简单工厂模式实现

// StrategyTest02.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
using namespace std;

//现金收费抽象类
class CashSuper
{
public:
    virtual double acceptCash(double money) = 0;
};

//正常收费类
class CashNormal : public CashSuper
{
public:
    double acceptCash(double money)
    {
        return money;
    }
};

//打折收费类
class CashRebate : public CashSuper
{
private :
    double rebate;
public :
    CashRebate(){};
    CashRebate(double rebate)
    {
        this->rebate = rebate;
    }
public:
    double acceptCash(double money)
    {
        return money * rebate;
    }
};

//返利收费类
class CashReturn : public CashSuper
{
private :
    double moneyContion;
    double moneyReturn;
public :

    CashReturn(){};
    CashReturn(double contion, double ret)
    {
        this->moneyContion = contion;
        this->moneyReturn = ret;
    }

    double acceptCash(double money)
    {
        double result = money;
        if(money > this->moneyContion)
        {
            result = money - this->moneyReturn * int(money / this->moneyContion);
        }
        return result;
    }
};

//收费工厂类
class CashFactory
{
public :
    static CashSuper* createCashAccept(char* type)
    {
        char* str1 = "正常收费";
        char* str2 = "满300返100";
        char* str3 = "打八折";

        CashSuper* cs = 0;
        if(strcmp(type, str1) == 0)
        {
            cs = new CashNormal;
        }        
        else if(strcmp(type, str2) == 0)
        {
            cs = new CashReturn(300, 100);
        }
        else if(strcmp(type, str3) == 0)
        {
            cs = new CashRebate(0.8);
        }

        return cs;
    }

};

int _tmain(int argc, _TCHAR* argv[])
{
    char* type[3] = {"正常收费", "满300返100", "打八折"};
    cout<<"选择收费方式"<<endl;
    for(int i=0; i<3; i++)
    {
        cout<<i<<" : "<<type[i]<<endl;
    }
    int num;
    cin>>num;
    
    double money;
    cout<<"请输入消费总额："<<endl;
    cin>>money;
    

    CashSuper* cs = CashFactory::createCashAccept(type[num % 3]);
    money = cs->acceptCash(money);
    cout<<"应收金额为："<<money<<endl;

    system("pause");
    return 0;
}

 3.策略与简单工厂结合

// StrategyTest03.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"



#include <iostream>
using namespace std;

//现金收费抽象类
class CashSuper
{
public:
    virtual double acceptCash(double money) = 0;
};

//正常收费类
class CashNormal : public CashSuper
{
public:
    double acceptCash(double money)
    {
        return money;
    }
};

//打折收费类
class CashRebate : public CashSuper
{
private :
    double rebate;
public :
    CashRebate(){};
    CashRebate(double rebate)
    {
        this->rebate = rebate;
    }
public:
    double acceptCash(double money)
    {
        return money * rebate;
    }
};

//返利收费类
class CashReturn : public CashSuper
{
private :
    double moneyContion;
    double moneyReturn;
public :

    CashReturn(){};
    CashReturn(double contion, double ret)
    {
        this->moneyContion = contion;
        this->moneyReturn = ret;
    }

    double acceptCash(double money)
    {
        double result = money;
        if(money > this->moneyContion)
        {
            result = money - this->moneyReturn * int(money / this->moneyContion);
        }
        return result;
    }
};
class CashContext
{
public :
    CashSuper* cs;
    CashContext(char* type)
    {
        char* str1 = "正常收费";
        char* str2 = "满300返100";
        char* str3 = "打八折";

        CashSuper* cs = 0;
        if(strcmp(type, str1) == 0)
        {
            cs = new CashNormal;
        }        
        else if(strcmp(type, str2) == 0)
        {
            cs = new CashReturn(300, 100);
        }
        else if(strcmp(type, str3) == 0)
        {
            cs = new CashRebate(0.8);
        }
    }

    double GetResult(double money)
    {
        return cs->acceptCash(money);
    }
};

int _tmain(int argc, _TCHAR* argv[])
{
    char* type[3] = {"正常收费", "满300返100", "打八折"};
    cout<<"选择收费方式"<<endl;
    for(int i=0; i<3; i++)
    {
        cout<<i<<" : "<<type[i]<<endl;
    }
    int num;
    cin>>num;
    
    double money;
    cout<<"请输入消费总额："<<endl;
    cin>>money;
    
    CashContext cc(type[num % 3]);
    money = cc.GetResult(money);

    cout<<"应收金额为："<<money<<endl;

    system("pause");
    return 0;
}