<?php
class DB{
private static $obj=null;
private function __construct(){
echo "链接数据库成功<br/>";
}
static function getInstance(){
if(is_null(self::$obj))
self::$obj=new self();
return self::$obj;
}
function query($sql){
echo $sql;
}
}
$db=DB::getInstance();
$db->query("select * from user");
?>
