FlyWeight模式

                  设计模式中的享元模式，避免大量拥有相同内容的小类的开销(如耗费内存),使大家共享一个类(元类).

                  使用面向对象的技术时，虽然在开发过程中能过简化设计，可是在一切是对象的思想下，在一些小粒度，大数量的应用中，可能会导致对象数极具增大，导致消耗太多的内存。比如文本编辑器，如果一个字符就是一个对象，那么可想而知对象数是对少。

                   FlyWeight模式就是用来解决这种问题的，同一个对象多次出现。实现是通过一个pool(对象池)来实现的，已有的对象直接使用，没有的创建使用，放进pool中。一般会实现会使用到Factory模式。

                  还有一种说法其实就是Factory+Singleton 。

                  下面是类图

代码实现：

 #ifndef FLYWEIGHT_H

#define FLYWEIGHT_H

#include <string>

#include <iostream>

class FlyWeight

{

public:

    FlyWeight(std::string _info);

    virtual ~FlyWeight(){}

    std::string getInfo() const {return info;}

    virtual void operator1() = 0;

private:

    std::string info;

};

#endif // FLYWEIGHT_H

#include "flyweight.h"

FlyWeight::FlyWeight(std::string _info):info(_info)

{

}

#ifndef CONCRETEFLYWEIGHT_H

#define CONCRETEFLYWEIGHT_H

#include "flyweight.h"

class ConcreteFlyWeight : public FlyWeight

{

public:

    ConcreteFlyWeight(std::string _info);

    ~ConcreteFlyWeight(){}

    void operator1(){}

};

#endif // CONCRETEFLYWEIGHT_H

#include "concreteflyweight.h"

ConcreteFlyWeight::ConcreteFlyWeight(std::string _info):FlyWeight(_info)

{

}

#ifndef FLYWEIGHTFACTORY_H

#define FLYWEIGHTFACTORY_H

#include "concreteflyweight.h"

#include <vector>

#include <string>

#include <iterator>

class FlyWeightFactory

{

public:

    FlyWeightFactory();

    ~FlyWeightFactory();

    int getPoolSize() const {return pool.size();}

    FlyWeight* getFlyWeight(const std::string key);

private:

    std::vector<FlyWeight*> pool;

};

#endif // FLYWEIGHTFACTORY_H

#include "flyweightfactory.h"

FlyWeightFactory::FlyWeightFactory()

{

}

FlyWeightFactory::~FlyWeightFactory()

{

    std::vector<FlyWeight*>::iterator ite;

    for (ite = pool.begin();ite != pool.end();++ite) {

        delete (*ite);

    }

    pool.clear();

}

FlyWeight* FlyWeightFactory::getFlyWeight(const std::string key)

{

    std::vector<FlyWeight*>::iterator ite;

    for (ite = pool.begin();ite != pool.end();++ite) {

        if ((*ite)->getInfo() == key) {

            return (*ite);

        }

    }

    FlyWeight * fly = new ConcreteFlyWeight(key);

    pool.push_back(fly);

    return fly;

}

#include <iostream>

using namespace std;

#include "flyweightfactory.h"

int main()

{

    FlyWeightFactory *p = new FlyWeightFactory;

    p->getFlyWeight("zhou");

    p->getFlyWeight("zhou");

    p->getFlyWeight("xiang");

    p->getFlyWeight("chenchen");

    p->getFlyWeight("chenchen");

    p->getFlyWeight("ZhouXiangLoveChenChen");

    p->getFlyWeight("ChenChenLoveZhouXiang");

    cout << p->getPoolSize()<<'\n';

    delete p;

    return 0;

}

运行结果：

在pool中的只有5个对象