PDO未定义的功能

I have this class:

<?php
    class LLPDO extends PDO{

         public function __construct($dsn, $user, $pass, $options = array()){
            $this->link = parent::__construct($dsn, $user, $pass, $options);
            $this->link->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        }

        public function isConnected(){
             try {
                $this->link->query('SELECT 1+1');
            } catch (PDOException $e) {
                return false;
            }
            return true;
        }

    }
?>

But when I make a call like so:

if(!$ibdb.isConnected()){
    $ibdb = new LLPDO(connectionString2($ini['ibdbn'], $ini['ibdbclient'], $ini['ibdbport']), $ini['ibdbusr'], $ini['ibdbpass'], array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION));
}

I get a Fatal error: Call to undefined function isConnected(). Am I calling the function wrong? Or did I do something incorrect in the class file? $ibdb was created ahead of time earlier in the script I'm running it in.

Methods are called through the -> operator:

if(!$ibdb->isConnected()){
    $ibdb = new LLPDO(connectionString2($ini['ibdbn'], $ini['ibdbclient'], $ini['ibdbport']), $ini['ibdbusr'], $ini['ibdbpass'], array(PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION));
}

if(!$ibdb.isConnected()){

. ? you should use arrow (->) to access methods/properties

if(!$ibdb->isConnected()){