设计模式之十七：单例模式(Singleton)

#include <iostream>

class Singleton
{
	public:
			//这里要将这个方法定义成静态的
			static Singleton * getInstance();
	private:
			Singleton()
			{

			}
	private:
			//静态成员函数只能操作静态成员变量，所以instance也应该是静态的
			static Singleton * instance;

};

//静态成员变量的初始化
Singleton * Singleton::instance=NULL;

Singleton * Singleton::getInstance()
{
				if(instance==NULL)
						instance=new Singleton();
				return instance;	
}

int main()
{
	Singleton *s1=Singleton::getInstance();
	Singleton *s2=Singleton::getInstance();
	if(s1==s2)
			std::cout<<"s1 and s2 are the same object"<<std::endl;

	return 0;
}

#include <iostream>
#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <string>
#include <vector>

using namespace std;

class LoadBalancer
{
	public:
			static LoadBalancer * getInstance();
			string getServer()
			{
				int i=rand()%5;
				return servers[i];
			}
	private:
			LoadBalancer()
			{
					servers.push_back("server I");
					servers.push_back("server II");
					servers.push_back("server III");
					servers.push_back("server IV");
					servers.push_back("server V");
			}	
	private:
			static	LoadBalancer * instance;
			vector<string> servers;
};

LoadBalancer * LoadBalancer::instance=NULL;

LoadBalancer * LoadBalancer::getInstance()
{
	if(instance==NULL)
			instance=new LoadBalancer();
	return instance;
}
int main()
{
	srand(time(0));
	LoadBalancer * load1=LoadBalancer::getInstance();
	LoadBalancer * load2=LoadBalancer::getInstance();

	cout<<load1->getServer()<<endl;
	cout<<load1->getServer()<<endl;
	cout<<load1->getServer()<<endl;
	cout<<load1->getServer()<<endl;
	cout<<load1->getServer()<<endl;
	cout<<load1->getServer()<<endl;
	cout<<load1->getServer()<<endl;
	cout<<load1->getServer()<<endl;
	cout<<load1->getServer()<<endl;
	cout<<load1->getServer()<<endl;
	cout<<load1->getServer()<<endl;
	cout<<load1->getServer()<<endl;

	delete load1;
	return 0;
}