Q:

Php OOP : Parent class values are always null

I have two php classes in two separate files:
File Name : ld.php 
<?php
  class LandDetail_Model{
     public function __construct() {}
     private $id;
     public $pId;
     private $bigha;
     private $katha;

function setId($id) { $this->id = $id; }
function getId() { return $this->id; }
function setPId($pId) { $this->pId = $pId; }
function getPId() { return $this->pId; }
function setBigha($bigha) { $this->bigha = $bigha; }
function getBigha() { return $this->bigha; }
function setKatha($katha) { $this->katha = $katha; }
?>

File Name :Land_Detail.php
<?php
    require_once '../models/ld.php';

    class LandDetail extends LandDetail_Model{
      public function __construct() {
            parent::__construct();
     }

  public function DoSomething(){
     echo "This is a value from Parent".$this->getPId();
  }
}
?>

Now in SomeFile.php I am doing something like this.
<?php
include 'Land_Detail.php';

$ld = new LandDetail();
$ld->setPId(10001);
$ld->DoSomething();

?>

Why $this->getPId() is always returning null value? What is wrong with my code here? What is the correct way to extend a class in php from different file?

A:

Why you write:
$ld->setPId = 10001;

Instead of
$ld->setPId(10001);

