<?php

class A 
{
private $a = 1;
}

class B extends A
{
private $a = 2;
}

class C extends B
{
public  $a = 3;
}

class D extends C  
{
public $a = 4;
}

var_dump(new A);
var_dump(new B);
var_dump(new C);
var_dump(new D);