python 设计模式之 单例模式

单例模式是做为"全局变量"的替代品出现的。所以它具有全局变量的特点：全局可见、贯穿应用程序的整个生命期，保证在程序执行中，某个类仅仅存在一个实例，所以通常不希望类中的构造函数被调用

python:

class Single(object):

	instance = None

	#

	def __init__(self):

		pass

	#

	def getInstance(self):

		if Single.instance == None:

			Single.instance = Single()

		return Single.instance

	#

	def printSelf(self):

		if Single.instance != None:

			print Single.instance

s = Single()

s1 = s.getInstance()

s2 = s.getInstance()

s1.printSelf()

s2.printSelf()</span>

C++:

Single.h

ifndef __SINGLE_H

#define __SINGLE_H

class Single

{

private:

	static Single *instance;

	Single();

public:

	static Single* getInstance();

	void printSelf();

};

#endif

Single.cpp

#include "Single.h"

#include <iostream>

Single* Single::instance = NULL;

Single::Single()

{

}

Single* Single::getInstance()

{

	if (!instance)

		instance = new Single;

	return instance;

}

void Single::printSelf()

{

	if (instance)

		std::cout << instance << std::endl;

}

#include "Single.h"

int main()

{

	Single::getInstance()->printSelf();

	Single *sin = Single::getInstance();

	sin->printSelf();

	return  0;

}