C++ 设计模式(八) FlyWeight模式

问题：

   在面向对象的设计过程中，可能需要创建创建许多对象，而实际上这些对象没有多大的区别，我们可以创建一个对象，让这许多对象共享一个对象，当然这些对象可能会有些许属性差异，我们可以通过调整这些属性来达到我们的要求。这样的好处是可以避免重复创建对象带来空间和时间的浪费。

 

UML：

 

 

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vector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.

flyweight.h

 

#ifndef FLYHEGIHT_H_#define FLYHEGIHT_H_#include <iostream>#include <string>using std::string;class FlyWeight{public: virtual void Operation(const string& strExnternalState); string GetState();protected:FlyWeight(string strState);private:string m_strState;};class ConcreteFlyWeight:public FlyWeight{public:ConcreteFlyWeight(string strState);void Operation(const string& strExternalState);protected:private:};#endif

 

flyweight.cpp

#include<iostream>#include<cstring>#include<string>#include "flyweight.h"using std::cout;using std::endl;using std::string;FlyWeight::FlyWeight(string strState){ this->m_strState=strState;}string FlyWeight::GetState(){return this->m_strState;}void FlyWeight::Operation(const string& strExternalState){ cout<<"internal State: "<<m_strState<<endl;}ConcreteFlyWeight::ConcreteFlyWeight(string strState):FlyWeight(strState){}void ConcreteFlyWeight::Operation(const string& strExternalState){cout<<"internal State: "<<GetState()<<",external state: "<<strExternalState<<endl;}

 

flyweightfactory.h

#ifndef FLYWEIGHTFACTORY_H_#define FLYWEIGHTFACTORY_H_#include<iostream>#include<vector>#include "flyweight.h"using namespace std;class FlyWeightFactory{public:FlyWeightFactory();virtual ~FlyWeightFactory();FlyWeight* GetFlyWeight(const string strState);protected:private:vector <FlyWeight*> m_vector;};#endif

 

flyweightfactory.h

 

#include <iostream>#include <string>#include <cstring>#include "flyWeightFactory.h"using std::cout;using std::endl;using std::string;FlyWeightFactory::FlyWeightFactory(){}FlyWeightFactory::~FlyWeightFactory(){}FlyWeight* FlyWeightFactory::GetFlyWeight(const string strState){vector<FlyWeight*>::iterator it=m_vector.begin();for(;it!=m_vector.end();it++){if((*it)->GetState()==strState){cout<<"alread created by user ..."<<endl;}return *it;}FlyWeight* flyweight=new ConcreteFlyWeight(strState);m_vector.push_back(flyweight);return flyweight;}

 

 

main.cpp

 

#include <iostream>#include<string>#include <cstring>#include "flyWeightFactory.h"using std::cout;using std::endl;using std::string;int main(int argc,char** argv){FlyWeightFactory* pFactory=new FlyWeightFactory();FlyWeight* pFlyWeight=pFactory->GetFlyWeight("hello"); pFlyWeight->Operation("good");pFlyWeight=pFactory->GetFlyWeight("world"); pFlyWeight->Operation("good");pFlyWeight=pFactory->GetFlyWeight("hello");pFlyWeight->Operation("good"); return 0;}