sql oop

<?php
class SQL
    {
        private $svr = "localhost";
        private $usr = "root";
        private $pwd = "";
        private $db = "buchjoin";

        public function __construct()
            {
                $svrU = $this->svr;
                $usrU = $this->usr;
                $pwdU = $this->pwd;
                $dbU = $this->db;
                $con = new mysqli($svrU, $usrU, $pwdU, $dbU);

                printf("Host info: %s\n", $con->host_info);

            }
    }
$a = 0;
$a = new SQL;
?>