设计模式(二)--策略模式(1)

策略模式(Strategy) ：

它定义了算法家族，分别封装起来,让他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。

结构图：

//Strategy抽象类，定义所有支持的算法的公共接口。 class Strategy { public: Strategy(){}; //算法方法 virtual void AlgorithmInterface(){}; }; //封装了具体算法或行为，继承于Strategy //具体算法A class ConcreteStrategyA : public Strategy { public: ConcreteStrategyA(){}; //算法A实现方法 virtual void AlgorithmInterface() { cout << "算法A实现方法" << endl; } }; //具体算法B class ConcreteStrategyB : public Strategy { public: ConcreteStrategyB(){}; //算法B实现方法 virtual void AlgorithmInterface() { cout << "算法B实现方法" << endl; } }; //具体算法C class ConcreteStrategyC : public Strategy { public: ConcreteStrategyC(){}; //算法C实现方法 virtual void AlgorithmInterface() { cout << "算法C实现方法" << endl; } }; //Context:用一个ConcreteStrategy来配置，维护一个对Strategy对象的引用 class Context { private: Strategy * m_strategy; public: Context(){}; //初始化时，传入具体的策略对象 Context(Strategy * strategy):m_strategy(strategy) { } //根据具体的策略对象，调用其算法的方法 void ContextInterface() { m_strategy->AlgorithmInterface(); } }; //客户端代码 int main() { Context * context; Strategy * m_strategy = new ConcreteStrategyA(); context = new Context(m_strategy); context->ContextInterface(); delete context; delete m_strategy; m_strategy = new ConcreteStrategyB(); context = new Context(m_strategy); context->ContextInterface(); delete context; delete m_strategy; m_strategy = new ConcreteStrategyC(); context = new Context(m_strategy); context->ContextInterface(); delete context; delete m_strategy; return 0; }

策略模式实现

#include "stdafx.h" #include "stdio.h" #include <memory> using namespace std; // 一个超市打折的实例 //抽象类 class CashSuper { public: virtual double acceptCash(double money) = 0; }; //正常收费子类 class CashNormal : public CashSuper { public: virtual double acceptCash(double money) { return money; } }; //打折收费子类 class CashRebate : public CashSuper { private: double moneyRebate; public: CashRebate(double Rebate = 0.0):moneyRebate(Rebate) { } virtual double acceptCash(double money) { return money * moneyRebate; } }; //返利收费子类 class CashReturn : public CashSuper { private: double moneyCondition; double moneyReturn; public: CashReturn(double Condition = 0.0, double Return = 0.0):moneyCondition(Condition), moneyReturn(Return) { } virtual double acceptCash(double money) { double result = money; if(money >= moneyCondition) result = money - (money / moneyCondition) * moneyReturn; return result; } }; class CashContext { private: auto_ptr<CashSuper> cs; public: CashContext(){}; //简单工厂模式和策略模式融合到一起 void createCashAccept(int type) { switch(type) { //正常收费 case 0: cs = auto_ptr<CashSuper> (new CashNormal()); break; case 1: cs = auto_ptr<CashSuper> (new CashReturn(300, 100)); break; case 2: cs = auto_ptr<CashSuper> (new CashRebate(0.8)); break; } } double GetResult(double money) { return cs->acceptCash(money); } }; int main(int argc, char* argv[]) { CashContext * cs = new CashContext(); cs->createCashAccept(0); printf("%2.2f/n",cs->GetResult(1000)); delete cs; return 0; }

总结：

策略模式是一种定义一系列算法的方法，从概念上来看，所有这些算法完成的都是相同的工作，只是实现不同，它可以以相同的方式调用所有的算法，减少了各种算法类与使用算法类之间的耦合。策略模式的Strategy类层次为Context定义了一系列的可供重用的算法行为。继承有助于析取出这些算法的公有功能。

另外一个策略模式的优点是简化了单元测试，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。

源文档 <http://blog.youkuaiyun.com/jia_xiaoxin/archive/2008/10/15/3081121.aspx>