gistfile1.txt

<?php
class PostBase {

  public $id;
  public $title;
  public $description;
  
  public function setID($id) {
    $this->id = $id;
  }
  
  final public function getID() {
    return $this->id;
  }
  
}

class Page extends PostBase {

  public function getPagePrefix() {
    return 'P.';
  }
  
}

class Item extends PostBase {

  public function getID() {
    return 'Item#'. $this->id;
  }
  
}