定义：

定义了算法族，分别封装起来，让它们之间可以互相替换，以此模式让算法的变化独立于使用算法的客户。

UML图：

代码实现：

/************************************************************************/
/*                           Strategy.h                                 */
/************************************************************************/

/**  
* @file Strategy.h  
* @brief Strategy模式的实现代码  
* @author wlq_729@163.com 
*      ://blog..net/rabbit729
* @version 1.0  
* @date 2009-02-23  
*/ 

#ifndef STRATEGY_H_
#define STRATEGY_H_
#include <string>
using std::string;

class IQuackBehavior
{
public:
    virtual string Quacking() = 0; 
};

class IFlyBehavior
{
public:
    virtual string Fly() = 0;
};

class MuteQuack : public IQuackBehavior
{
public:
    string Quacking();
};

class Quack : public IQuackBehavior
{
public:
    string Quacking();
};

class Squeak : public IQuackBehavior
{
public:
    string Quacking();
};

class FlyNoWay : public IFlyBehavior
{
public:
    string Fly();
};

class FlyRocketPowered : public IFlyBehavior
{
public:
    string Fly();
};

class FlyWithWings : public IFlyBehavior
{
public:
    string Fly();
};

class Duck
{
protected:
    IFlyBehavior* flyBehavior;
    IQuackBehavior* quackBehavior;

public:

    void SetFly(IFlyBehavior* flyBehavior);
    void SetQuack(IQuackBehavior* quackBehavior);
    virtual string Display() = 0;
    string PerformFly();
    string PerformQuack();
    string Swim();
};

class MallardDuck : public Duck
{
public:
    MallardDuck();
    string Display();
};

class ModelDuck : public Duck
{
public:
    ModelDuck();
    string Display();
};

class RubberDuck : public Duck
{
public:
    RubberDuck();
    string Display();
};
#endif

/************************************************************************/
/*                           Strategy.cpp                               */
/************************************************************************/

/**  
* @file Strategy.cpp  
* @brief Strategy模式的实现代码  
* @author wlq_729@163.com 
*      ://blog..net/rabbit729
* @version 1.0  
* @date 2009-02-23  
*/ 

#include "Strategy.h"

string MuteQuack::Quacking()
{
    return "silence";
}

string Quack::Quacking()
{
    return "Quack";
}

string Squeak::Quacking()
{
    return "Squeak";
}

string FlyNoWay::Fly()
{
    return "I can't fly.";
}

string FlyRocketPowered::Fly()
{
    return "I'm flying with a rocket!";
}

string FlyWithWings::Fly()
{
    return "I'm flying!!";
}

void Duck::SetFly(IFlyBehavior *flyBehavior)
{
    this->flyBehavior = flyBehavior;
}

void Duck::SetQuack(IQuackBehavior* quackBehavior)
{
    this->quackBehavior = quackBehavior;
}

string Duck::PerformFly()
{
    return flyBehavior->Fly();
}

string Duck::PerformQuack()
{
    return quackBehavior->Quacking();
}

string Duck::Swim()
{
    return "All ducks float, even decoys!";
}

MallardDuck::MallardDuck()
{
    quackBehavior = new Quack();
    flyBehavior = new FlyWithWings();
}

string MallardDuck::Display()
{
    return "I'm a real Mallard duck";
}

ModelDuck::ModelDuck()
{
    quackBehavior = new Quack();
    flyBehavior = new FlyNoWay();
}

string ModelDuck::Display()
{
    return "I'm a model duck";
}

RubberDuck::RubberDuck()
{
    quackBehavior = new Squeak();
    flyBehavior = new FlyNoWay();
}

string RubberDuck::Display()
{
    return "I'm a rubber duck";
}

/************************************************************************/
/*                           test.cpp                                   */
/************************************************************************/

/**  
*
*/ 

#include "Strategy.h"
#include <iostream>
using namespace std;

void main(void)
{
    Duck* duck = new MallardDuck();
    cout<<duck->PerformQuack()<<endl;
    cout<<duck->PerformFly()<<endl;

    duck->SetFly(new FlyRocketPowered());
    cout<<duck->PerformFly()<<endl;
}

程序输出：

Quack

I'm flying!!

I'm flying with a rocket!

请按任意键继续. . .