<?php
class foo{

    protected $fooVariable;

    function __construct(){
      $this->fooVariable = "hello world";
      $this->changeVariable();
    }
    function changeVariable(){
      $this->fooVariable = "goodbye world";
      $this->echoVariable();
    }
    function echoVariable(){
      echo $this->fooVariable;
    }
}
$a = new foo;

goodbye world