设计模式:可复用面向对象软件的基础 书中对 Strategy 模式的定义如下:
定义了一系列的算法,把它们一个个封装起来,并且使它们可相互替换。本模式使得算法可独立于它的用户而变化。
案例:设计一个商场收银软件,营业员根据客户所购买商品的单价和数量,向客户收费。商场有许多促销的策略,打折,满300减100等。。。
1. 如果采用之前将的工厂模式,可以采用如下的方式编写:
// Last Update:2014-03-17 21:05:53 /** * @file cash.h * @brief Strategy Pattern * @author shoulinjun@126.com * @version 0.1.00 * @date 2014-03-17 */ #ifndef CASH_H #define CASH_H #include <string> #include <iostream> #include <sstream> #include <cmath> // base class // define interface class CashSuper { public: virtual ~CashSuper() {} virtual double acceptCash(double money) = 0; }; class CashNormal : public CashSuper { public: double acceptCash(double money){ return money; } }; class CashRebate : public CashSuper{ public: CashRebate(std::string moneyRate = "0.0"){ std::stringstream s(moneyRate); s >> this->moneyRate_; } double acceptCash(double money){ return money * moneyRate_; } private: double moneyRate_; }; class CashReturn : public CashSuper{ public: CashReturn(std::string moneyCondition, std::string moneyReturn){ std::stringstream s(moneyCondition); s >> this->moneyCondition_; std::stringstream s2(moneyReturn); s2 >> this->moneyReturn_; } double acceptCash(double money){ if(money >= moneyCondition_){ money -= std::floor(money / moneyCondition_) * moneyReturn_; } return money; } private: double moneyCondition_, moneyReturn_; }; // factory class class CashFactory{ public: static CashSuper* createCashSuper(std::string type) { CashSuper *pCashSuper(NULL); if(type == "正常收费"){ pCashSuper = new CashNormal(); } else if(type == "满300减100"){ pCashSuper = new CashReturn("300", "100"); } else if(type == "打8折"){ pCashSuper = new CashRebate("0.8"); } else{ return NULL; } return pCashSuper; } }; #endif /*CASH_H*/ #include "cash.h" #include <iostream> #include "boost/shared_ptr.hpp" using namespace std; int main(void) { boost::shared_ptr<CashSuper> pCashSuper(CashFactory::createCashSuper("正常收费")); cout << pCashSuper->acceptCash(300) << endl; pCashSuper = boost::shared_ptr<CashSuper>(CashFactory::createCashSuper("打8折")); cout << pCashSuper->acceptCash(300) << endl; pCashSuper = boost::shared_ptr<CashSuper>(CashFactory::createCashSuper("满300减100")); cout << pCashSuper->acceptCash(300) << endl; return 0; }
2. Strategy 模式
策略模式可以减少各种算法类与使用算法类之间的耦合;
简化单元测试,因为每个算法都有自己的类,可以通过自己的接口进行单元测试。// base class // define interface class CashSuper { public: virtual ~CashSuper() {} virtual double acceptCash(double money) = 0; }; class CashNormal : public CashSuper { public: double acceptCash(double money){ return money; } }; class CashRebate : public CashSuper{ public: CashRebate(std::string moneyRate = "0.0"){ std::stringstream s(moneyRate); s >> this->moneyRate_; } double acceptCash(double money){ return money * moneyRate_; } private: double moneyRate_; }; class CashReturn : public CashSuper{ public: CashReturn(std::string moneyCondition, std::string moneyReturn){ std::stringstream s(moneyCondition); s >> this->moneyCondition_; std::stringstream s2(moneyReturn); s2 >> this->moneyReturn_; } double acceptCash(double money){ if(money >= moneyCondition_){ money -= std::floor(money / moneyCondition_) * moneyReturn_; } return money; } private: double moneyCondition_, moneyReturn_; }; class CashContext{ public: CashContext(std::string type): pCashSuper_(NULL){ if(type == "正常收费"){ pCashSuper_ = new CashNormal; } else if(type == "满300减100"){ pCashSuper_ = new CashReturn("300", "100"); } else if(type == "打8折"){ pCashSuper_ = new CashRebate("0.8"); } // else } ~CashContext(){ if(pCashSuper_) delete pCashSuper_; } double GetResult(double money){ assert(pCashSuper_ != NULL); return pCashSuper_->acceptCash(money); } private: CashSuper *pCashSuper_; // copy not allowed CashContext(const CashContext&); CashContext& operator=(const CashContext&); }; // 客户端使用如下: CashContext csuper("满300减100"); cout << csuper.GetResult(300) << endl;
参考资料:
1. 大话设计模式
2. 设计模式:可复用面向对象软件的基础
Design Patterns---- Strategy 模式,布布扣,bubuko.com
Design Patterns---- Strategy 模式
原文:http://blog.csdn.net/shoulinjun/article/details/21403877