设计模式—享元模式（二十二）

        软件领域中的设计模式的重要性不言而喻。设计模式中运用了面向对象编程语言的重要特性：封装、继承、多态。虽然知道这些特性的定义但是并没有做到真正的理解，这样特性有什么作用？用于什么场合中等等问题，带着疑问开始学习设计模式，主要参考《大话设计模式》和《设计模式:可复用面向对象软件的基础》两本书。

        享元模式（Flyweight），运用共享技术有效地支持大量细粒度的对象。



        FlyweightFactory：一个享元工厂，用来创建并管理Flyweight对象，它主要是用来确保合理地共享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）
        Flyweight：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。
        ConcreteFlyweight：继承Flyweight超类或者实现Flyweight接口，并为内部状态增加存储空间。
        UnshareConcreteFlyweight：指那些不需要共享的Flyweight子类，因为Flyweight接口共享成为可能，但它并不强制共享。

#include <iostream>
#include <string>
#include <vector>
#include<map>
using namespace std;
class Flyweight
{
public:
virtual void Operation(int extrinsicState) = 0;
};
class ConcreteFlyweight :public Flyweight
{
public:
virtual void Operation(int extrinsicState) override
{
cout << "具体共享的Flyweight：" << extrinsicState << endl;
}
};
//不需共享的Flyweight子类
class UnshareConcreteFlyweight :public Flyweight
{
public:
virtual void Operation(int extrinsicState) override
{
cout << "不共享的Flyweight：" << extrinsicState << endl;
}
};

//享元工厂
class FlyweightFactory
{
private:
map<string, ConcreteFlyweight*> m_hash;
public:
FlyweightFactory()
{
m_hash["X"] = new ConcreteFlyweight();
m_hash["Y"] = new ConcreteFlyweight();
m_hash["Z"] = new ConcreteFlyweight();
}
Flyweight* GetFlyweight(string key)
{
return m_hash[key];
}
};

//客户端
int main()
{
int extrsicstate = 22;

FlyweightFactory* f = new FlyweightFactory();
Flyweight* fx = f->GetFlyweight("X");
fx->Operation(extrsicstate++);

Flyweight* fy = f->GetFlyweight("X");
fy->Operation(extrsicstate++);

Flyweight* fz = f->GetFlyweight("X");
fz->Operation(extrsicstate++);

UnshareConcreteFlyweight* uf = new UnshareConcreteFlyweight();
uf->Operation(extrsicstate++);

return 0;
}