Flyweight模式

Flyweight（享元）模式

在开发时，如果创建很多对象，就会造成很大的内存开销，特别是大量轻量级(细粒度)的对象，还会造成内存碎片．Flyweight模式就是运用共享技术，有效支持大量细粒度对象的设计模式．

其类结构图如下：

在FlyweightFactory中有一个管理，存储对象的对象池，当调用GetFlyweight时会首先遍历对象池，如果已存在，则返回，否则创建新对象添加到对象池中．有些对象可能不想被共享，那么就使用UnShareConcreteFlyweight.

实现： /Flyweight.h

//Flywight.h #ifndef _FLYWEIGHT_H_ #define _FLYWEIGHT_H_ #include<string> using std::string; 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); }; #endif

//Flyweight.cpp

//Flyweight.cpp #include"Flyweight.h" #include<iostream> using std::cout; Flyweight::Flyweight(string intrinsicState) { _intrinsicState = intrinsicState; } Flyweight::~Flyweight() {} void Flyweight::Operation(const string& extrinsicState) {} string Flyweight::GetIntrinsicState() { return _intrinsicState; } ConcreteFlyweight::ConcreteFlyweight(string intrinsicState) :Flyweight(intrinsicState) { cout << "ConcreteFlyweight Build..." << std::endl; } ConcreteFlyweight::~ConcreteFlyweight() {} void ConcreteFlyweight::Operation(const string& extrinsicState) { cout << "ConcreteFlyweight:内蕴[" << this->GetIntrinsicState() << "]外蕴[" << extrinsicState << "]" << std::endl; }

//FlyweightFactory.h

//FlyweightFactory.h #ifndef _FLYWEIGHTFACTORY_H_ #define _FLYWEIGHTFACTORY_H_ #include"Flyweight.h" #include<string> #include<vector> using std::string; using std::vector; class FlyweightFactory { public: FlyweightFactory(); ~FlyweightFactory(); Flyweight* GetFlyweight(const string& key); private: vector<Flyweight*> _fly; }; #endif

//FlyweightFactory.cpp

//FlyweightFactory.cpp #include"FlyweightFactory.h" #include<iostream> #include<string> #include<cassert> using std::string; using std::cout; FlyweightFactory::FlyweightFactory() {} FlyweightFactory::~FlyweightFactory() {} Flyweight* FlyweightFactory::GetFlyweight(const string& key) { vector<Flyweight*>::iterator it = _fly.begin(); for (; it != _fly.end(); it++) { if ((*it)->GetIntrinsicState() == key) { cout << "already create by users..." << std::endl; return *it; } } Flyweight* fn = new ConcreteFlyweight(key); _fly.push_back(fn); return fn; }

//main.cpp

#include"Flyweight.h" #include"FlyweightFactory.h" int main() { FlyweightFactory* fc = new FlyweightFactory(); Flyweight* fw1 = fc->GetFlyweight("hello"); Flyweight* fw2 = fc->GetFlyweight("world"); Flyweight* fw3 = fc->GetFlyweight("hello"); return 0; }