设计模式——策略模式（Strategy）

• 定义：封装一系列算法, 使其可相互替换。
• 本模式使算法可独立于客户而变化。
• UML

  

• 代码示例（C++）

  //==========================================
  //strategy.h
  //==========================================
  #pragma once
  
  class Strategy;
  class Context
  {
  public:
      Context(Strategy* pStrategy);
      ~Context();
      void SetStrategy(Strategy* pStrategy);
      void Request();
  private:
      Strategy* m_pStrategy;
  };
  
  class Strategy
  {
  public:
      virtual ~Strategy(){}
      virtual void AlgorithmInterface() = 0;
  };
  
  class ConcreteStrategyA : public Strategy
  {
  public:
      void AlgorithmInterface();
  };
  
  class ConcreteStrategyB : public Strategy
  {
  public:
      void AlgorithmInterface();
  };
  
  //==========================================
  //strategy.cpp
  //==========================================
  #include "strategy.h"
  #include <iostream>
  using namespace std;
  
  Context::Context(Strategy* pStrategy)
      :m_pStrategy(pStrategy)
  {
  }
  
  Context::~Context()
  {
      delete m_pStrategy;
  }
  
  void Context::SetStrategy(Strategy* pStrategy)
  {
      delete m_pStrategy;
      m_pStrategy = pStrategy;
  }
  
  void Context::Request()
  {
      if (NULL != m_pStrategy)
      {
          m_pStrategy->AlgorithmInterface();
      }
  }
  
  void ConcreteStrategyA::AlgorithmInterface()
  {
      cout<<"ConcreteStrategyA::AlgorithmInterface()"<<endl;
  }
  
  void ConcreteStrategyB::AlgorithmInterface()
  {
      cout<<"ConcreteStrategyB::AlgorithmInterface()"<<endl;
  }
  
  int main()
  {
      Context ctx(new ConcreteStrategyA);
      ctx.Request();
      ctx.SetStrategy(new ConcreteStrategyB);
      ctx.Request();
  
      return 0;
  }