问调用未定义的方法时，它是静态的和存在的？

EN

php > require_once('System.php');
php > System::users();
PHP Fatal error:  Call to undefined method System::users() in php shell code on line 1

<?php
require_once('System.php');
var_dump(System::users());
?>

php > echo (class_exists('System')) ? 'THERE!' : 'WHERE?';
WHERE?
php > require_once('System.php');
php > echo (class_exists('System')) ? 'THERE!' : 'WHERE?';
THERE!
php > System::users();
PHP Fatal error:  Call to undefined method System::users() in php shell code on line 1

<?php
class System
{
    public static function users()
    {
        $users = array();

        if( !$data_array = file('/etc/passwd') )
        {
            return false;
        }

        foreach( $data_array as $line )
        {
            $data = explode(":", $line);
            $user = array_shift($data);

                list(, $uid, $gid, $info, $path, $terminal) = $data;

            $tmp = array();
            $tmp['uid'] = $uid;
            $tmp['gid'] = $gid;
            $tmp['name'] = array_shift(explode(',', $info));
            $tmp['path'] = $path;
            $tmp['terminal'] = $terminal;

            $users[$user] = $tmp;

            unset($tmp);
        }

        return $users;
    }

    public static function user( $user )
    {
        $users = self::users();

        if( array_key_exists($user, $users) )
        {
            return $users[$user];
        }
        else
        {
            return false;
        }
    }
}
?>