如何使用php实现封装数据库的类文件

class dbname{
    private $localhost;
    private $root;
    private $pass;
    private $db_name;
public function __construct($localhost,$root,$pass,$db_name){
    $this->localhost=$localhost;
    $this->root=$root;
    $this->pass=$pass;
    $this->db_name=$db_name;
    $this->query();
}
    private function query(){
        mysql_connect($this->localhost,$this->root,$this->pass);
        mysql_select_db($this->db_name);
        mysql_query("set names utf8");
    } 
}
?>