享元模式c++代码实现

享元--程序中会使用到大量的对象，这些对象耗费大量的内存，这些对象有相同的
地方(内部的状态)可以共享，可以用一个简单工厂类去返回已经存在的对象，不存
在的则创建，这些对象用一个容器存放。使用对象时可以再传入外部的状态。

 

// flyweight.cpp : 定义控制台应用程序的入口点。
//

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

class Flyweight
{
public:
	
	//map会使用空构造
	Flyweight()
	{

	}
	Flyweight(string intrinsicState)
	{
		this->intrinsicState = intrinsicState;
	}
	virtual void operation(string extrinsicState)
	{
		cout << "Flyweight::operation()" << endl;
	}
	string intrinsicState;
};
class ConcreteFlyweight:public Flyweight
{
public:
	ConcreteFlyweight(string intrinsicState):Flyweight(intrinsicState)
	{
		
	}
	void operation(string extrinsicState)
	{
		cout << "intrinsicState: " << this->intrinsicState << endl;
		cout << "extrinsicState: " << extrinsicState << endl;
	}
};
class FlyweightFactory
{
public:
	//静态成员函数要使用静态成员
	static FlyweightFactory *getInstance()
	{
		if(f == NULL)
		{
			f = new FlyweightFactory();
		}
		return f;
	}
	Flyweight * getFlyweight(string intrinsicState)
	{
		if(1 != m.count(intrinsicState))
		{
			//要使用多态，这里要放指针,放对象不行
			m[intrinsicState] = new ConcreteFlyweight(intrinsicState);
		}
		return m[intrinsicState];
	}
	~FlyweightFactory()
	{
		cout << "~FlyweightFactory" << endl;
		//new的内存要释放
		if(!m.empty())
		{
			map<string,Flyweight *>::iterator it = m.begin();
			while(it != m.end())
			{
				cout << it->first << endl;
				delete it->second;
				it++;
			}
		}
		/* 这个代码要注释掉，因为main中的fc与这里的f指的是相同的内存，
		在delete时，先调用析构函数，会释放一遍内存，完了delete还要再释放一遍
		
		if(NULL != f)
		{
			delete f;
			f = NULL;
		}
		*/
	}
protected:
	FlyweightFactory()
	{
		f = NULL;
		m.clear();
	}
	
	
	static FlyweightFactory *f;
	map<string,Flyweight*> m;
};
//静态成员初始化
FlyweightFactory * FlyweightFactory::f = NULL;
int main()
{
	FlyweightFactory *fc = FlyweightFactory::getInstance();
	Flyweight *f1 = fc->getFlyweight("f1");
	Flyweight *f2 = fc->getFlyweight("f2");
	Flyweight *f3 = fc->getFlyweight("f1");
	f1->operation("o1");
	f2->operation("o2");
	f3->operation("o3");
	delete fc;
	return 0;
}