Observer Pattern in PHP

In this example, we'll be creating a stock ticker demo that uses the Observer Pattern to broadcast stock symbols out to observers. If an observer is looking for a particular stock symbol, it will update the price that is also sent across.

   <?php

   // Stock ticker observer:

   class TickerObserver
   {
       // The symbol that this observer will monitor for:
       private $symbol;
       // The last price observed:
       private $lastPrice;

       function __construct($symbol)
       {
           $this->symbol = $symbol;
           $this->lastPrice = 0.0;
       }

       // Recieves an update from the subject:
       public function Update($symbol, $price)
       {
           if($this->symbol === $symbol)
           {
               $this->lastPrice = $price;
           }
       }

       // Used to get the most recent update information:
       public function GetTicker()
       {
           return "{$this->symbol} : {$this->lastPrice}";
       }
   }

   class StockTicker
   {
       // The subscribed observers:
       private $observers = array();

       function __construct()
       {   }

       // Adds an observer to the list:
       public function AttachObserver($observer)
       {
           $this->observers[] = $observer;
       }

       // Notifies all observers:
       public function Notify($symbol, $price)
       {
           foreach($this->observers as $observer)
           {
               $observer->Update($symbol, $price);
           }
       }

   }