PHP Scope / encapsulation example

<?php
/**
 * Define MyClass
 */
const PHP_BR = "<br/>";
const PHP_SPACE = " ";

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

    function printHello()
    {
        echo $this->public, PHP_SPACE. __CLASS__,PHP_BR;
        echo $this->protected,PHP_SPACE. __CLASS__,PHP_BR;
        echo $this->private,PHP_SPACE. __CLASS__,PHP_BR;
    }
}
class sub extends MyClass{
    public function __construct()
    {   
        echo $this->public, PHP_SPACE.__CLASS__,PHP_BR;
        echo  $this->protected,PHP_SPACE. __CLASS__,PHP_BR;
        echo $this->private ?? "private  not access" , PHP_SPACE. __CLASS__,PHP_BR;
    }
}

$obj = new sub();
echo $obj->public,PHP_SPACE.'object',PHP_BR; // Works
echo $obj->private ?? "object   not access private" , PHP_SPACE. __CLASS__,PHP_BR;
echo $obj->protected ?? "object  not access protected" , PHP_SPACE. __CLASS__,PHP_BR;
 
 // Fatal Error
$obj->printHello(); // Shows Public, Protected and Private