设计模式----Strategy(策略)

作用:

　　定义一系列的算法,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使用它的客户而变化.

　　解析:

　　简而言之一句话,Strategy模式是对算法的封装.处理一个问题的时候可能有多种算法,这些算法的接口(输入参数,输出参数等)都是一致的,那么可以考虑采用Strategy模式对这些算法进行封装,在基类中定义一个函数接口就可以了.

#include <iostream>
using namespace std;

class Strategy
{
public:
virtual ~Strategy(){}

virtual void AlgorithmInterface() = 0;
};

class Context
{
public:
Context(Strategy *pStrategy) : m_pStrategy(pStrategy)
{
}

~Context()
{
delete m_pStrategy;
m_pStrategy = NULL;
}

void ContextInterface()
{
if (NULL != m_pStrategy)
{
m_pStrategy->AlgorithmInterface();
}
}
private:
Strategy* m_pStrategy;
};

class ConcreteStrategyA : public Strategy
{
public:
virtual ~ConcreteStrategyA(){}

virtual void AlgorithmInterface()
{
cout << "AlgorithmInterface Implemented by ConcreteStrategyA\n";
}
};

class ConcreteStrategyB : public Strategy
{
public:
virtual ~ConcreteStrategyB(){}

virtual void AlgorithmInterface()
{
cout << "AlgorithmInterface Implemented by ConcreteStrategyB\n";
}
};

class ConcreteStrategyC : public Strategy
{
public:
virtual ~ConcreteStrategyC(){}

virtual void AlgorithmInterface()
{
cout << "AlgorithmInterface Implemented by ConcreteStrategyC\n";
}
};
void main()
{
Strategy* pStrategy = new ConcreteStrategyA();
Context* pContextA = new Context(pStrategy);
pContextA->ContextInterface();
delete pContextA;

pStrategy = new ConcreteStrategyB();
Context* pContextB = new Context(pStrategy);
pContextB->ContextInterface();
delete pContextB;

pStrategy = new ConcreteStrategyC();
Context* pContextC = new Context(pStrategy);
pContextC->ContextInterface();
delete pContextC;
}