~$ more hide.php
<?php
class Foo {
        private $data = array('Foo'=>array('Bar'=>'Quux'));
        function Foo() {
                echo $this->data['Foo']['Bar'];
        }
}
$f = new Foo();
Foo::$data['Foo']['Bar'];
?>
~$ php hide.php
Quux
Fatal error: Cannot access private property Foo::$data in /home/yango/hide.php on line 9