设计模式C++实现二：策略模式

策略模式(strategy): 定义算法家族，分别封装起来，让这些算法直接可以相互替换，我们可以自由添加或者修改算法而不会影响客户.

优点：简化了单元测试，因为每个算法都有自己的类，可以通过自己的接口单独测试。

如果我们在客户端为了判断使用哪个算法而使用switch语句来分析，我们可以使用策略模式把这个判断的过程隐藏到后台，把每个算法用一个strategy类实现。这样就简化了客户端的代码，也隐藏了实现的细节。

#ifndef STRATEGY_H#define STRATEGY_H#include<iostream>using namespace std;class CashSuper{friend class CashContext;protected:virtual double acceptCash(double money) = 0;};/*工厂模式class CashContext{CashSuper *cs;public:CashContext(CashSuper *cashs) :cs(cashs){}void operator =(CashSuper * re){cs = re;}double GetResult(double money){return cs->acceptCash(money);}};*/class CashContext{CashSuper *cs;char StrategyType;public:CashContext(){}CashContext(char &SType);void operator =(char &SType);double GetResult(double money){if (cs == NULL){ cout << "The strategy is unfind."; return -1; }return cs->acceptCash(money);}};class CashNormal:public CashSuper{//friend class CashContext;public:double acceptCash(double money){return money;}};class CashRebate:public CashSuper{//friend class CashContext;double Rebate;public:CashRebate(double discount) :Rebate(discount){}double acceptCash(double money){return money*Rebate;}};class CashReturn :public CashSuper{//friend class CashContext;double baseCash,returnCash;public:CashReturn(double baseC,double returnC) :baseCash(baseC),returnCash(returnC) {}double acceptCash(double money){if (money >= baseCash) return money - returnCash;return money;}};CashContext::CashContext(char &SType) :StrategyType(SType){switch (StrategyType){case('a') :case('A') :  cs = new CashNormal;break;case('b') :case('B') :  cs = new CashRebate(0.8);break;case('c') :case('C') :  cs = new CashReturn(1000, 200);break;default:cs = NULL;break;}}void CashContext::operator =(char &SType){StrategyType = SType;switch (StrategyType){case('a') :case('A') :  cs = new CashNormal;break;case('b') :case('B') :  cs = new CashRebate(0.8);break;case('c') :case('C') :  cs = new CashReturn(1000, 200);break;default:cs = NULL;break;}}#endif

#include"strategy.h"int main(){double ShouldPay = 1520;/*   简单工厂模式的实现，下面的三种策略的细节暴露在客户端CashNormal cashn;CashRebate cashrb(0.95);CashReturn cashrt(1000, 200);CashContext cashC(&cashn);cout << "The real pay is : " << cashC.GetResult(ShouldPay) << endl;cashC=&cashrb;cout << "The real pay is : " << cashC.GetResult(ShouldPay) << endl;cashC=&cashrt;cout << "The real pay is : " << cashC.GetResult(ShouldPay) << endl;*///下面实现的是用策略模式实现的，其付款细节在客户端是不可见的，如果要添加或者删除策略//我们可以在strategy.h中添加该策略类，然后把这个类添加到CashContext中实现，这样在客户端//很少要修改信息，实现细节的隐藏cout << "Please enter the strategy type,'a' or 'A' instand the normalcash ,\n"<< "'b' or 'B' instand the rebatecash, 'c' or 'C' instand the returncash.\n";char type;CashContext cashC;while (cin >> type){cashC = type;cout << "The real pay is : " << cashC.GetResult(ShouldPay) << endl;}return 0;}

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