022 --- 第26章 享元模式

简述：

　　享元模式：运用共享技术有效地支持大量细粒度的对象。

　　享元模式包括：享元工厂类、享元接口类、具体享元类

　　　　享元工厂类：　用来创建并管理享元接口类对象，它主要使用来确保合理地共享享元接口类，当用户请求一个享元接口类对象时，享元工厂类对象提供一个已创建的实例或者创建一个（不存在的话）

　　　　享元接口类：所有具体享元类的超类或接口，通过这个接口可以接受并作用于外部状态。

　　　　具体享元类：指那些不需要共享的享元接口类的子类，因为享元接口类共享成为可能，但它并不强制共享。

享元模式：

#include <iostream>
#include <map>
using namespace std;

// 享元接口类
class CFlyweight
{
public:
    virtual void Operation(int nExtrinsicstate) = 0;
};

// 具体享元类
class CConcreteFlyweight : public CFlyweight
{
public:
    virtual void Operation(int nExtrinsicstate) { cout << "具体Flyweight：" << nExtrinsicstate << endl; }
};

// 不需要共享的享元子类
class CUnsharedConcreteFlyWeight : public CFlyweight
{
public:
    virtual void Operation(int nExtrinsicstate) { cout << "不共享的具体Flyweight：" << nExtrinsicstate << endl; }
};

// 享元工厂类
class CFlyweightFactory
{
private:
    map<string, CFlyweight*> m_mapFlyweights;

public:
    CFlyweightFactory()
    {
        m_mapFlyweights.insert(make_pair("X", new CConcreteFlyweight()));
        m_mapFlyweights.insert(make_pair("Y", new CConcreteFlyweight()));
        m_mapFlyweights.insert(make_pair("Z", new CConcreteFlyweight()));
    }

    ~CFlyweightFactory()
    {
        map<string, CFlyweight*>::iterator ite = m_mapFlyweights.begin();
        while (ite != m_mapFlyweights.end())
        {
            if((*ite).second)
            {
                delete (*ite).second;
                (*ite).second = NULL;
            }
                
            ++ite;
        }

        m_mapFlyweights.clear();
    }

    CFlyweight* GetFlyweight(string szKey) { return m_mapFlyweights[szKey]; }
};


int main()
{
    int nExtrinsicstate = 22;

    CFlyweightFactory FlyweightFactory;

    CFlyweight* fx = FlyweightFactory.GetFlyweight("X");
    fx->Operation(--nExtrinsicstate);

    CFlyweight* fy = FlyweightFactory.GetFlyweight("Y");
    fy->Operation(--nExtrinsicstate);

    CFlyweight* fz = FlyweightFactory.GetFlyweight("Z");
    fz->Operation(--nExtrinsicstate);

    CUnsharedConcreteFlyWeight uf;
    uf.Operation(--nExtrinsicstate);

    system("pause");
    return 0;
}

输出结果：

例：网站共享代码

代码如下：

#include <iostream>
#include <map>
using namespace std;

// 用户类
class CUser
{
private:
    string m_szName;

public:
    CUser(string szName) { m_szName = szName; }

    string GetName() { return m_szName; }
};

// 网站基类（享元接口类）
class CWebSite
{
public:
    virtual void Use(CUser* pUser) = 0;
};

// 具体网站类（具体享元类）
class CConcreteWebSite : public CWebSite
{
private:
    string m_szName;

public:
    CConcreteWebSite(string szName) { m_szName = szName; }

    virtual void Use(CUser* pUser) { cout << "网站分类： " + m_szName << " 用户： " + pUser->GetName() << endl; }
};

// 网站工厂类（享元工厂类）
class CWebSiteFactory
{
private:
    map<string, CWebSite*> m_mapWebSites;

public:
    ~CWebSiteFactory()
    {
        map<string, CWebSite*>::iterator ite = m_mapWebSites.begin();
        while (ite != m_mapWebSites.end())
        {
            if ((*ite).second)
            {
                delete (*ite).second;
                (*ite).second = NULL;
            }
            ++ite;
        }
        m_mapWebSites.clear();
    }

    // 获得网站分类
    CWebSite* GetWebSiteCategory(string szKey)
    {
        if (!m_mapWebSites[szKey])
            m_mapWebSites[szKey] = new CConcreteWebSite(szKey);

        return m_mapWebSites[szKey];
    }

    // 获得网站分类总数
    int GetWebSiteCount() { return m_mapWebSites.size(); }
};


int main()
{
    CWebSiteFactory WebSiteFactory;

    CWebSite* fx = WebSiteFactory.GetWebSiteCategory("产品展示");
    fx->Use(&CUser("GHL"));

    CWebSite* fy = WebSiteFactory.GetWebSiteCategory("产品展示");
    fy->Use(&CUser("GGG"));

    CWebSite* fz = WebSiteFactory.GetWebSiteCategory("产品展示");
    fz->Use(&CUser("HHH"));

    CWebSite* fl = WebSiteFactory.GetWebSiteCategory("博客");
    fl->Use(&CUser("LLL"));

    CWebSite* fm = WebSiteFactory.GetWebSiteCategory("博客");
    fm->Use(&CUser("ggg"));

    CWebSite* fn = WebSiteFactory.GetWebSiteCategory("博客");
    fn->Use(&CUser("hhh"));

    cout << "网站分类总数为： " << WebSiteFactory.GetWebSiteCount() << endl;

    system("pause");
    return 0;
}