常见设计模式的解析和实现(C++)之十三-FlyWeight模式

作用:

运用共享技术有效地支持大量细粒度的对象。

UML结构图:



解析:

Flyweight 模式在大量使用一些可以被共享的对象的时候经常使用.比如,在QQ聊天的时候很多时候你懒得回复又不得不回复的时候,一般会用一些客套的话语敷衍别人,如 "呵呵","好的"等等之类的,这些简单的答复其实每个人都是提前定义好的,在使用的时候才调用出来.Flyweight就是基于解决这种问题的思路而产 生的,当需要一个可以在其它地方共享使用的对象的时候,先去查询是否已经存在了同样的对象,如果没有就生成之有的话就直接使用.因此,Flyweight 模式和Factory模式也经常混用.

实现:

需要说明的是下面的实现仅仅实现了对可共享对象的使用,非可共享对象的使用没有列 出,因为这个不是Flyweight模式的重点.这里的实现要点是采用一个list链表来保存这些可以被共享的对象,需要使用的时候就到链表中查询是不是 已经存在了,如果不存在就初始化一个,然后返回这个对象的指针.

1)Flyweight.h


/********************************************************************


created: 2006/07/26


filename: FlyWeight.h


author: 李创


http://www.cppblog.com/converse/




purpose: FlyWeight模式的演示代码


*********************************************************************/




#ifndef FLYWEIGHT_H


#define FLYWEIGHT_H




#include <string>


#include <list>




typedef std::string STATE;




class Flyweight




{


public:




virtual ~Flyweight()

{}




STATE GetIntrinsicState();


virtual void Operation(STATE& ExtrinsicState) = 0;




protected:


Flyweight(const STATE& state)


:m_State(state)






{


}




private:


STATE m_State;


};




class FlyweightFactory




{


public:




FlyweightFactory()

{}


~FlyweightFactory();




Flyweight* GetFlyweight(const STATE& key);




private:


std::list<Flyweight*> m_listFlyweight;


};




class ConcreateFlyweight


: public Flyweight




{


public:


ConcreateFlyweight(const STATE& state)


: Flyweight(state)






{


}




virtual ~ConcreateFlyweight()

{}




virtual void Operation(STATE& ExtrinsicState);


};




#endif




/**/






2)Flyweight.cpp


/********************************************************************


created: 2006/07/26


filename: FlyWeight.cpp


author: 李创


http://www.cppblog.com/converse/




purpose: FlyWeight模式的演示代码


*********************************************************************/




#include "FlyWeight.h"


#include <iostream>




inline STATE Flyweight::GetIntrinsicState()




{


return m_State;


}




FlyweightFactory::~FlyweightFactory()




{


std::list<Flyweight*>::iterator iter1, iter2, temp;




for (iter1 = m_listFlyweight.begin(), iter2 = m_listFlyweight.end();


iter1 != iter2;


)






{


temp = iter1;


++iter1;


delete (*temp);


}




m_listFlyweight.clear();


}




Flyweight* FlyweightFactory::GetFlyweight(const STATE& key)




{


std::list<Flyweight*>::iterator iter1, iter2;




for (iter1 = m_listFlyweight.begin(), iter2 = m_listFlyweight.end();


iter1 != iter2;


++iter1)






{


if ((*iter1)->GetIntrinsicState() == key)






{


std::cout << "The Flyweight:" << key << " already exits"<< std::endl;


return (*iter1);


}


}




std::cout << "Creating a new Flyweight:" << key << std::endl;


Flyweight* flyweight = new ConcreateFlyweight(key);


m_listFlyweight.push_back(flyweight);


}




void ConcreateFlyweight::Operation(STATE& ExtrinsicState)




{




}




/**/








3)Main.cpp


/********************************************************************


created: 2006/07/26


filename: Main.cpp


author: 李创


http://www.cppblog.com/converse/




purpose: FlyWeight模式的测试代码


*********************************************************************/




#include "FlyWeight.h"




int main()




{


FlyweightFactory flyweightfactory;


flyweightfactory.GetFlyweight("hello");


flyweightfactory.GetFlyweight("world");


flyweightfactory.GetFlyweight("hello");




system("pause");


return 0;


}


/**/