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 <iostream> using std::cout; using std::endl; //定义行为类 void FlyWithWings::fly(){ cout<<"I'm flying with wings!!"<<endl; } void FlyNoWay::fly(){ cout<<"I can't fly5555!!"<<endl; } void FlyRocketPowerd::fly(){ cout<<"I'm flying with a ROCKET!!"<<endl; } void Quack::quack(){ cout<<"Quack!!!"<<endl; } void Squeak::quack(){ cout<<"Squeak!!!"<<endl; } void MuteQuack::quack(){ cout<<"MuteQuack!!!"<<endl; } //定义Duck类的成员方法 void Duck::swim(){ cout<<"I'm swimming!!!"<<endl; } void Duck::performQuack(){ quackBehavior->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!!!"<<endl; } MallardDuck::MallardDuck(){ flyBehavior=new FlyWithWings; quackBehavior=new Quack; } //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!!
