PHP子类对象不能直接访问父类的属性

今天再看PHP手册时候发现一个问题，那就是PHP子类对象不能直接访问父类的属性，这实在让人疑惑，现在先记录，以后看有什么解释没有。例子：

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::$public,PHP_EOL; //此时，会报错，Uncaught Error: Access to undeclared static property: MyClass::$public 

    }

}

$obj2 = new MyClass2();

$obj2->printHello2();