public static function get_fiefdoms($user_id='') {

                if (!isset($this) && !$user_id) { echo "Not an instance"; return false; }   

------------------
$user = new User($GLOBALS['user']->id);
if (get_class($user) == 'User') { echo "User Var is a User Class Object"; }
$fiefdoms = $user->get_fiefdoms();

----------------------
User Var is a User Class Object 
Not an instance