享元模式(Flyweight):运用共享技术有效地支持大量细粒度的对象。
四个角色类:
Flyweight享元类:所有具体享元类的超类或接口,通过这个接口,Flyweight可以接受并作用于外部状态。
Flyweight享元工厂类:一个享元工厂,用来创建并管理Flyweight,当用户请求一个Flyweight时,FlyweightFactory对象提供一个已创建的实例或者创建一个(如果不存在的话)。
ConcreteFlyweight具体享元类:继承Flyweight超类或实现Flyweight接口,并为内部状态增加存储空间。
UnSharedConcreteFlyweight不需共享的具体Flyweight子类、指那些不需要共享的Flyweight子类。因为Flyweight接口类共享成为可能,但并不强制共享。
模式实现:
[code]//享元类 class Flyweight{ public: virtual void Operation(int extrinsicState){} }; //具体享元类 class ConcreteFlyweight: public Flyweight{ public: virtual void Operation(int extrinsicState)override{ std::cout << "ConcreteFlyweight: " << extrinsicState << std::endl; } }; //不需共享的Flyweight子类 class UnSharedConcreteFlyweight: public Flyweight{ public: virtual void Operation(int extrinsicState){ std::cout << "UnSharedConcreteFlyweight: " << extrinsicState << std::endl; } }; //享元工厂,用来创建并管理Flyweight对象 class FlyweightFactory{ private: std::map<std::string, Flyweight*> flyweights; public: FlyweightFactory(){ flyweights["X"] = new ConcreteFlyweight; flyweights["Y"] = new ConcreteFlyweight; flyweights["Z"] = new ConcreteFlyweight; } Flyweight* GetFlyweight(std::string key){ return (Flyweight*)flyweights[key]; } };
客户端:
[code]//Client int main(){ //外部状态 int extrinsicState = 22; //工厂 FlyweightFactory *f = new FlyweightFactory; Flyweight* fx = f->GetFlyweight("X"); fx->Operation(--extrinsicState); //Output: ConcreteFlyweight: 21 Flyweight* fy = f->GetFlyweight("Y"); fy->Operation(--extrinsicState); //Output: ConcreteFlyweight: 20 Flyweight* fz = f->GetFlyweight("Z"); fz->Operation(--extrinsicState); //Output: ConcreteFlyweight: 19 Flyweight *uf = new UnSharedConcreteFlyweight; //Output: UnSharedConcreteFlyweight: 18 uf->Operation(--extrinsicState); return 0; }
享元模式好处:
如果一个应用程序使用了大量的对象,而大量的这些对象造成了很大的存储开销时就应该考虑使用。
对象的大多数状态可以使用外部状态,如果删除对象的外部状态,那么可以用相对较少的共享对象取代很多组对象,此时可以考虑使用享元模式。
以上就是C++设计模式浅识享元模式的内容,更多相关内容请关注PHP中文网(www.php.cn)!