策略模式定义了算法家族。分别封装起来。让它们之间能够相互替换，此模式让算法的变化独立于使用算法的客户。

Head First设计模式中介绍策略模式时以Duck类作为样例。当中用flyBehavior和quackBehavior两个接口引用变量代表鸭子飞行和鸭子叫这两种行为，通过改变flyBehavior和quackBehavior来满足不同的Duck子类的不同行为。这样带来的优点就是能够在执行时改变Duck子类的行为。以下是我用C++改写的代码。

//MyDuck.h#ifndef MYDUCK_INCLUDED#define MYDUCK_INCLUDED//在这里我用抽象类取代原文中的接口class FlyBehavior{	public:		virtual void fly()=0;};class QuackBehavior{	public:		virtual void quack()=0;};class FlyWithWings:public FlyBehavior{	public:		void fly();};class FlyNoWay:public FlyBehavior{	public:		void fly();};class FlyRocketPowerd:public FlyBehavior{	public:		void fly();};class Quack:public QuackBehavior{	public:		void quack();};class Squeak:public QuackBehavior{	public:		void quack();};class MuteQuack:public QuackBehavior{	public:		void quack();};class Duck{	public:		Duck();		void swim();		virtual void display()=0;		void performQuack();		void performFly();		void setQuackBehavior(QuackBehavior *newBehavior);		void setFlyBehavior(FlyBehavior *newBehavior);	//在这里我用基类指针取代原文中的接口引用变量	protected:		FlyBehavior *flyBehavior;		QuackBehavior *quackBehavior;};class MallardDuck:public Duck{	public:		virtual void display();		MallardDuck();};#endif // MYDUCK_INCLUDED

MyDuck.cpp#include "MyDuck"#include 
     
      using std::cout;using std::endl;//定义行为类void FlyWithWings::fly(){	cout<<"I'm flying with wings!!"<
      
       quack();}void Duck::performFly(){	flyBehavior->fly();}void Duck::setFlyBehavior(FlyBehavior *newBehavior){	flyBehavior=newBehavior;}void Duck::setQuackBehavior(QuackBehavior *newBehavior){	quackBehavior=newBehavior;}Duck::Duck(){}//定义MallardDuck类的成员方法void MallardDuck::display(){	cout<<"I'm MallardDuck!!!"<
      
     

//MyDuckMain.cpp#include "MyDuck"int main(){	Duck *mallard=new MallardDuck;	mallard->display();	mallard->performFly();	mallard->performQuack();	mallard->swim();	mallard->setFlyBehavior(new FlyNoWay);	mallard->performFly();	mallard->setFlyBehavior(new FlyRocketPowerd);	mallard->performFly();	return 0;}

执行结果为：

I'm MallardDuck!!!

I'm flying with wings!!

Quack!!!

I'm swimming!!!

I can't fly5555!!

I'm flying with a ROCKET!!

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