PHP design mode OBSERVER (Observer mode)

Copy CodeThe code is as follows:
<?php
/**
* Observer mode
*
* Defines a one-to-many dependency between objects so that when an object's state changes, all objects that depend on it are notified and automatically refreshed
* The ability to easily create objects that view the state of the target object, and to provide the specified functionality that is not coupled to the core object
* Plug-in System
*/
Class Observerable
{
Private $_observers = Array ();

Public Function Registerobserver ($observer)
{
$this->_observers[] = $observer;
}

Public Function Removeobserver ($observer)
{
$key = Array_search ($observer, $this->_observers);
if (!) ( $key = = False))
{
unset ($this->_observers[$key]);
}
}

Public Function Notifyobservers ()
{
foreach ($this->_observers as $observer)
{
if ($observer instanceof observer) $observer->update ($this);
}
}
}

Interface Observer
{
Public Function Update ($observer);
}

Interface Displayelement
{
Public function display ();
}

--Instance class definition
Class Newsobserverable extends Observerable
{
Private $_sports_news;
Public Function setsportsnews ($data)
{
$this->_sports_news = $data;
$this->notifyobservers ();
}

Public Function Getsportsnews ()
{
return $this->_sports_news;
}

Private $_local_news;
Public Function setlocalnews ($data)
{
$this->_local_news = $data;
$this->notifyobservers ();
}

Public Function Getlocalnews ()
{
return $this->_local_news;
}
}

Class Sportsnews implements Observer,displayelement
{
Private $_data = null;
Public Function Update ($observer)
{
if ($this->_data!= $observer->getsportsnews ())
{
$this->_data = $observer->getsportsnews ();
$this->display ();
}
}

Public Function display ()
{
echo $this->_data.date ("y-m-d h:i:s"). " <br/> ";
}
}

Class LocalNews implements Observer,displayelement
{
Private $_data = null;
Public Function Update ($observer)
{
if ($this->_data!= $observer->getlocalnews ())
{
$this->_data = $observer->getlocalnews ();
$this->display ();
}
}

Public Function display ()
{
echo $this->_data.date ("y-m-d h:i:s"). " <br/> ";
}
}

--Materialized---

$objObserver = new Newsobserverable ();
$local = new LocalNews ();
$sports = new Sportsnews ();

$objObserver->registerobserver ($local);
$objObserver->registerobserver ($sports);

$objObserver->setsportsnews ("Sports News 1");
$objObserver->setlocalnews ("local news 1");
$objObserver->removeobserver ($sports);
$objObserver->setlocalnews ("Local news 2");
$objObserver->setsportsnews ("Sports News 2");
$objObserver->removeobserver ($local);
$objObserver->setlocalnews ("local news 3");