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

 1 #include <iostream>
 2 #include "FlyBehavior.h"
 3
 4 class Duck
 5 {
 6 private:
 7     FlyBehavior *m_p_fly_behavior;
 8 public:
 9     virtual void quack() { std::cout << "--quack--" << std::endl; }
10     virtual void swim() { std::cout << "--swim--" << std::endl; }
11     virtual void display() { std::cout << "--duck--" << std::endl; }
12
13     virtual void fly() { if ( NULL != m_p_fly_behavior) { m_p_fly_behavior->fly(); } };
14     void set_fly_behavior( FlyBehavior *p_fly_behavior) { m_p_fly_behavior = p_fly_behavior; }
15
16     Duck() : m_p_fly_behavior(NULL) {}
17     virtual ~Duck() { if (m_p_fly_behavior) { delete m_p_fly_behavior; } }
18 };

MallardDuck.h

1 #include "Duck.h"
2 #include "FlyWithWings.h"
3
4 class MallardDuck : public Duck
5 {
6 public:
7     void display() { std::cout << "--MallardDuck--" << std::endl; }
8     MallardDuck() { set_fly_behavior( new FlyWithWings() ); }
9 };

RedheadDuck.h

1 #include "FlyWithWings.h"
2 class RedheadDuck : public Duck
3 {
4 public:
5     void display() { std::cout << "--RedheadDuck--" << std::endl; }
6     RedheadDuck() { set_fly_behavior( new FlyWithWings() ); }
7 };

RubberDuck.h

1 #include "FlyNoWay.h"
2
3 class RubberDuck : public Duck
4 {
5 public:
6     void display() { std::cout << "--RubberDuck--" << std::endl; }
7     void quack() { std::cout << "--squeak--" << std::endl; }
8     RubberDuck() { set_fly_behavior( new FlyNoWay() ); }
9 };

再来看看FlyBehavior类及其子类

FlyBehavior.h

1 #include <iostream>
2
3 class FlyBehavior
4 {
5 public:
6     virtual void fly() {};
7     virtual ~FlyBehavior() {};
8 };

FlyWithWings.h

1 #include "FlyBehavior.h"
2
3 class FlyWithWings : public FlyBehavior
4 {
5 public:
6     void fly () { std::cout << "--fly with wings--" << std::endl; }
7 };

FlyNoWay.h

1 #include "FlyBehavior.h"
2
3 class FlyNoWay : public FlyBehavior
4 {
5 public:
6     void fly() { std::cout << "--can not fly--" << std::endl; }
7 };

最后是主函数

main.cpp

 1 #include "MallardDuck.h"
 2 #include "RedheadDuck.h"
 3 #include "RubberDuck.h"
 4 #include <vector>
 5
 6 void test()
 7 {
 8     std::vector<Duck *> p_ducks;
 9     p_ducks.push_back( new MallardDuck() );
10     p_ducks.push_back( new RedheadDuck() );
11     p_ducks.push_back( new RubberDuck() );
12
13     for (std::vector<Duck *>::iterator it = p_ducks.begin(); it < p_ducks.end(); it ++)
14     {
15         std::cout << std::endl;
16         (*it)->display();
17         (*it)->quack();
18         (*it)->swim();
19         (*it)->fly();
20         delete (*it);
21     }
22 }
23
24 int main()
25 {
26     while (true)
27     {
28         test();
29     }
30 }

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。