what is the error using OOPS with PDO
class DB
{
    public $dbh;
    private $qry;

    public function __construct($user ='root',$pass = '')
    {
        try {
            $this->dbh = new PDO('mysql:host=localhost;dbname=parixan',$user,$pass);
            $this->dbh->exec("SET CHARACTER SET utf8");
            echo "connected";
        } catch(Exception $e){
            die("Unable to connect: " . $e->getMessage());
        }
    }
}

class User
{
    public $db;
    protected $_table ='tbl_user';
    public function __construct($dbh)
    {
        $this->db = $dbh;
    }
    public function getUserDetails($id) //line #10
    {
        $qry = "SELECT * FROM $this->_table WHERE id = :userID LIMIT 1";
        $stmt = $this->db->prepare($qry); //line #13
        $stmt->bindParam(':userID',$id,PDO::PARAM_INT);
        if ($stmt->execute()) {
        while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
            echo "<pre>";print_r($row);
        }
    }

    }

}

include_once('class.user.php');
include_once('class.db.php');
$dbh = new DB();
$obj_user = new User($dbh);
$obj_user ->getUserDetails(1);

public function prepare($qry) {
    return $this->dbh->prepare($qry);
}