php的单例模式

　　单例模式一般会用在数据库连接上

具体代码例子：

<?php
class Mysql {
    private $conn;
    private static $instance =null;
    private function __construct(){
        $conn = @mysql_connect('localhost','root','root');
    }
    //单例模式
    public  static function getInstance (){
        if(! self::$instance instanceof self){
            self::$instance = new self;
        }
        return self::$instance;     
    } 
    //防止克隆
    private function __clone(){}
}


$mysql  = Mysql::getInstance();
$mysql2  = Mysql::getInstance();
var_dump($mysql);
echo '<hr>';
var_dump($mysql2);