大话设计模式26----享元模式

大话设计模式

1 享元模式（Flyweight）结构图

2 对享元模式的一些解释

概念：运用共享技术有效的支持大量细粒度的对象。【DP】

Flyweight类：是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。

class Flyweight
{
public:
	virtual void Operatiron(int extrinsicstate) = 0;
};

ConcreteFlyweight类：继承Flyweight类或实现Flyweight接口，并为内部状态增加存储空间。

class ConcreteFlyweight :public Flyweight
{
public:
	void Operatiron(int extrinsicstate) override
	{
		cout << "具体Flyweight" << extrinsicstate << endl;
	}
};

UnsharedFlyweight类，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。

class UnsharedFlyweight :public Flyweight
{
public:
	void Operatiron(int extrinsicstate) override
	{
		cout << "不共享的具体Flyweight" << extrinsicstate << endl;
	}
};

FlyweightFactory类：一个共享工厂，用来创建并管理Flyweight对象。它主要用来确保合理的共享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。（不一定非得这样，完全可以在需要时判断是否为空来决定是否实例化）

class FlyweightFactory
{
private:
	Hashtable *flyweight = new Hashtable();

public:
	FlyweightFactory()
	{
		flyweight.Add("X", new ConcreteFlyweight());//用法错误，这里只是表示出这种形式
		flyweight.Add("Y", new ConcreteFlyweight());
		flyweight.Add("Z", new ConcreteFlyweight());
	}

	Flyweight *GetFlyweight(string key)
	{
		return (Flyweight *)flyweight[key];
	}
};

客户端代码：

int main()
{
	int extrinsicstate = 22;

	FlyweightFactory *f = new FlyweightFactory();

	Flyweight *fx = f->GetFlyweight("X");
	fx->Operatiron(--extrinsicstate);

	Flyweight *fy = f->GetFlyweight("Y");
	fx->Operatiron(--extrinsicstate);

	Flyweight *fz = f->GetFlyweight("Z");
	fx->Operatiron(--extrinsicstate);

	Flyweight *uf = new UnsharedFlyweight();
	uf->Operatiron(--extrinsicstate);

	return 0;
}

优点：

享元模式可以避免大量非常相似类的开销。在程序设计中，有时需要生成大量细粒度的类实例来表示数据。如果能发现这些实例除了几个参数外基本上都是相同的，有时就能够大幅度的减少需要实例化的类的数量。如果能把那些参数移到类实例的外面，在方法调用时将它们传递进来，就可以通过共享大幅度地减少单个实例的数目。

也就是说，享元模式Flyweight执行时所需的状态是有内部的也可能有外部的，内部状态存储于ConcreteFlyweight对象之中，而外部对象则应该考虑由客户端对象存储或计算，当调用Flyweight对象的操作时，将该状态传递给它。

应用场景：

• 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是外部状态，如果删除对象的外部状态（客户端代码），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。

3 C++源代码实现

3.1  源代码结构图

3.2 C++源代码

User.h

#ifndef _USER_H_
#define _USER_H_

#include
using std::string;

class User
{
private:
	string name;

public:
	User(string name)
	{
		this->name = name;
	}

	string getName()
	{
		return this->name;
	}
};

#endif

Flyweight.h（Website类）

#ifndef _FLYWEIGHT_H_
#define _FLYWEIGHT_H_

#include"User.h"
#include
using std::string;

class Flyweight
{
public:
	virtual void Operation(User &user) = 0;
};	

class ConcreteFlyweight:public Flyweight
{
private:
	string name;

public:
	ConcreteFlyweight(string name);
	void Operation(User &user) override;
};

#endif

Flyweight.cpp（Website.cpp）

#include
#include"Flyweight.h"

using std::cout;
using std::endl;

ConcreteFlyweight::ConcreteFlyweight(string name)
{
	this->name = name;
}

void ConcreteFlyweight::Operation(User &user)
{
	cout << "网站分类:\t" << name << ";\t用户：" << user.getName() << endl;
}

FlyweightFactory.h(ConcreteWebsite.h)

#include
#include

FlyweightFactory.cpp(ConcreteFactory.cpp)

#include"Flyweight.h"
#include"FlyweightFactory.h"

FlyweightFactory::~FlyweightFactory()
{
	for (auto &m : (*mmap))
	{
		delete m.second;
	}

	delete mmap;
}


Flyweight *FlyweightFactory::GetGlyweightGategory(string key)
{
	for (const auto &m : (*mmap))
	{
		if (m.first == key)
			return m.second;
	}

	(*mmap)[key] = new ConcreteFlyweight(key);
	
	return (*mmap)[key];
}

int FlyweightFactory::GetFlywightCount()
{
	return mmap->size();
}

客户端Client.h

#include"Flyweight.h"
#include"FlyweightFactory.h"
#include
using std::cout;
using std::endl;

int main()
{
	FlyweightFactory *f = new FlyweightFactory();

	Flyweight *fx1 = f->GetGlyweightGategory("产品展示");
	fx1->Operation(User("小菜"));

	Flyweight *fx2 = f->GetGlyweightGategory("产品展示");
	fx2->Operation(User("大鸟"));

	Flyweight *fx3 = f->GetGlyweightGategory("产品展示");
	fx3->Operation(User("娇娇"));

	Flyweight *fb1 = f->GetGlyweightGategory("博客");
	fb1->Operation(User("老顽童"));

	Flyweight *fb2 = f->GetGlyweightGategory("博客");
	fb2->Operation(User("桃谷六仙"));

	Flyweight *fb3 = f->GetGlyweightGategory("博客");
	fb3->Operation(User("南海鳄神"));

	cout << "网站分类个数" << f->GetFlywightCount() << endl;

	delete f;

	system("pause");
	return 0;
}

运行结果：

网站分类:       产品展示;       用户：小菜
网站分类:       产品展示;       用户：大鸟
网站分类:       产品展示;       用户：娇娇
网站分类:       博客;   用户：老顽童
网站分类:       博客;   用户：桃谷六仙
网站分类:       博客;   用户：南海鳄神
网站分类个数2
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