PHP子類對象不能直接訪問父類的屬性嗎

class MyClass
{
    public $public = 'Public';
    protected $protected = 'Protected';
    private $private = 'Private';

    function printHello()
    {
        echo "This is Myclass".PHP_EOL;
        echo $this->public.PHP_EOL;
        echo $this->protected,PHP_EOL;
        echo $this->private,PHP_EOL;
    }
}
class MyClass2 extends MyClass
{
    public $public = 'Publi2c';
    protected $protected = 'Protected2';
    
    function printHello2()
    {
        echo $this->public.PHP_EOL;
        echo $this->protected,PHP_EOL;
        echo parent::$public,PHP_EOL; //這里報錯了。Uncaught Error: Access to undeclared static         
                                       //property: MyClass::$public
    }
}

$obj2 = new MyClass2();
$obj2->printHello2();

請問我注釋這里為什么出錯了？