php单例模式

<?php
/**
* by www.phpddt.com
*/
class Mysql{
//该属性用来保存实例
private static $conn;
//构造函数为private,防止创建对象
private function __construct(){
$this->conn = mysql_connect('localhost','root','');
}
//创建一个用来实例化对象的方法
public static function getInstance(){
if(!(self::$conn instanceof self)){
self::$conn = new self;
}
return self::$conn;
}
//防止对象被复制
private function __clone(){
trigger_error('Clone is not allowed !');
}

}
//只能这样取得实例，不能new 和 clone
$mysql = Mysql::getInstance();
?>