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.csdn.net/jia_xiaoxin/archive/2008/10/15/3081121.aspx>