Flyweight Pattern

1.Flyweight 模式以共享的方式高效的支持大量的细粒度对象，对象分为内部状态、外部状态。将可以被共享的状态作为内部状态存储在对象中，而外部状态在适当的时候作为参数传递给对象。

当以下所有的条件都满足时，可以考虑使用享元模式：

一个系统有大量的对象。
这些对象耗费大量的内存。
这些对象的状态中的大部分都可以外部化。
这些对象可以按照内蕴状态分成很多的组，当把外蕴对象从对象中剔除时，每一个组都可以仅用一个对象代替。
软件系统不依赖于这些对象的身份，换言之，这些对象可以是不可分辨的。

2.Flyweight模式结构图（不想被共享的对象UnshaerConcreteFlyweight，暂不讨论）

3.实现

 #ifndef _FLYWEIGHT_H_

 #define _FLYWEIGHT_H_

 #include <string>

 using namespace std;

 class Flyweight

 {

 public:

     virtual ~Flyweight();

     virtual void Operation(const string& extrinsicState);

     string GetIntrinsicState();

 protected:

     Flyweight(string intrinsicState);

 private:

     string _intrinsicState;

 };

 class ConcreteFlyweight:public Flyweight

 {

 public:

     ConcreteFlyweight(string intrinsicState);

     ~ConcreteFlyweight();

     void Operation(const string& extrinsicState);

 protected:

 private:

 }; 

 #endif

Flyweight.h

 #include "Flyweight.h"

 #include <iostream>

 using namespace std;

 Flyweight::Flyweight(string intrinsicState)

 {

     this->_intrinsicState = intrinsicState;

 }

 Flyweight::~Flyweight()

 {

 }

 void Flyweight::Operation(const string& extrinsicState)

 {

 }

 string Flyweight::GetIntrinsicState()

 {

     return this->_intrinsicState;

 }

 ConcreteFlyweight::ConcreteFlyweight(string intrinsicState):Flyweight(intrinsicState)

 {

     cout<<"ConcreteFlyweight Build....."<<intrinsicState<<endl;

 }

 ConcreteFlyweight::~ConcreteFlyweight()

 {

 }

 void ConcreteFlyweight::Operation(const string& extrinsicState)

 {

     cout<<"ConcreteFlyweight:内蕴["<<this->GetIntrinsicState()<<"] 外蕴["<<extrinsicState<<"]"<<endl;

 }

Flyweight.cpp

 #ifndef _FLYWEIGHTFACTORY_H_

 #define _FLYWEIGHTFACTORY_H_

 #include "Flyweight.h"

 #include <string>

 #include <vector>

 using namespace std;

 class FlyweightFactory

 {

 public:

     FlyweightFactory();

     ~FlyweightFactory();

     Flyweight* GetFlyweight(const string& key);

 protected:

 private:

     vector<Flyweight*> _fly;

 }; 

 #endif

FlyweightFactory.h

 #include "FlyweightFactory.h"

 #include <iostream>

 #include <string>

 #include <cassert>

 using namespace std;

 using namespace std;

 FlyweightFactory::FlyweightFactory()

 {

 }

 FlyweightFactory::~FlyweightFactory()

 {

 }

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

 {

     vector<Flyweight*>::iterator it = _fly.begin();

     for (; it != _fly.end();it++)

     { //找到了，就一起用，^_^

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

         {

             cout<<"already created by users...."<<endl;

             return *it;

         }

     }

     Flyweight* fn = new ConcreteFlyweight(key);

     _fly.push_back(fn);

     return fn;

 }

FlyweightFactory.cpp

 #include "Flyweight.h"

 #include "FlyweightFactory.h"

 #include <iostream>

 using namespace std;

 int main(int argc,char* argv[])

 {

     FlyweightFactory* fc = new FlyweightFactory();

     Flyweight* fw1 = fc->GetFlyweight("hello");

     Flyweight* fw2 = fc->GetFlyweight("world!");

     Flyweight* fw3 = fc->GetFlyweight("hello");

     return ;

 }

main.cpp

巴特西

Flyweight Pattern

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