Headfirst设计模式的C++实现——策略模式(Strategy)

前言

最近在学习《Headfirst设计模式》，里面的例子都是Java的。但是我对Java并不熟悉，所以试着用C++来实现书中的例子。

先来看看Duck以及子类

Duck.h

 #include <iostream>
 #include "FlyBehavior.h"

 class Duck
 {
 private:
     FlyBehavior *m_p_fly_behavior;
 public:
     virtual void quack() { std::cout << "--quack--" << std::endl; }
     virtual void swim() { std::cout << "--swim--" << std::endl; }
     virtual void display() { std::cout << "--duck--" << std::endl; }

     virtual void fly() { if ( m_p_fly_behavior) { m_p_fly_behavior->fly(); } };
     void set_fly_behavior( FlyBehavior *p_fly_behavior) { m_p_fly_behavior = p_fly_behavior; }

     Duck() : m_p_fly_behavior(NULL) {}
     virtual ~Duck() { if (m_p_fly_behavior) { delete m_p_fly_behavior; } }
 };

MallardDuck.h

 #include "Duck.h"
 #include "FlyWithWings.h"

 class MallardDuck : public Duck
 {
 public:
     void display() { std::cout << "--MallardDuck--" << std::endl; }
     MallardDuck() { set_fly_behavior( new FlyWithWings() ); }
 };

RedheadDuck.h

 #include "FlyWithWings.h"
 class RedheadDuck : public Duck
 {
 public:
     void display() { std::cout << "--RedheadDuck--" << std::endl; }
     RedheadDuck() { set_fly_behavior( new FlyWithWings() ); }
 };

RubberDuck.h

 #include "FlyNoWay.h"

 class RubberDuck : public Duck
 {
 public:
     void display() { std::cout << "--RubberDuck--" << std::endl; }
     void quack() { std::cout << "--squeak--" << std::endl; }
     RubberDuck() { set_fly_behavior( new FlyNoWay() ); }
 };

再来看看FlyBehavior类及其子类

FlyBehavior.h

 #include <iostream>

 class FlyBehavior
 {
 public:
     virtual void fly() {};
     virtual ~FlyBehavior() {};
 };

FlyWithWings.h

 #include "FlyBehavior.h"

 class FlyWithWings : public FlyBehavior
 {
 public:
     void fly () { std::cout << "--fly with wings--" << std::endl; }
 };

FlyNoWay.h

 #include "FlyBehavior.h"

 class FlyNoWay : public FlyBehavior
 {
 public:
     void fly() { std::cout << "--can not fly--" << std::endl; }
 };

最后是主函数

main.cpp

 #include "MallardDuck.h"
 #include "RedheadDuck.h"
 #include "RubberDuck.h"
 #include <vector>

 void test()
 {
     std::vector<Duck *> p_ducks;
     p_ducks.push_back( new MallardDuck() );
     p_ducks.push_back( new RedheadDuck() );
     p_ducks.push_back( new RubberDuck() );

     for (std::vector<Duck *>::iterator it = p_ducks.begin(); it < p_ducks.end(); it ++)
     {
         std::cout << std::endl;
         (*it)->display();
         (*it)->quack();
         (*it)->swim();
         (*it)->fly();
         delete (*it);
     }
 }

 int main()
 {
     while (true)
     {
         test();
     }
 }

稍作解释

main函数中死循环的调用test函数的意图是测试以上实现有没有内存泄露。