Parse error: syntax error, unexpected T_VARIABLE, expecting T_FUNCTION

Could someone tell me what I'm doing wrong?

I want to display the users online on specific rooms only.

the code below is the function that calls my online.php this is under my chat.php
when I load the page this function also loads.

function whos_online(){
 if (window.XMLHttpRequest){xmlhttp=new XMLHttpRequest();}
 else{xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");}
 xmlhttp.open("GET","online.php?room=<?php $_SESSION['room']?>",false);
 xmlhttp.send();
 document.getElementById("whos_online").innerHTML=xmlhttp.responseText; 
 }
 

ONLINE.PHP

this is the content of my online.php

<link rel="stylesheet" type="text/css" href="style.css" />
 <?php
 
 session_start();
 include 'db.inc.php';
 
 class WhosOnline{
 $rn = $_GET['room'];
 protected $get_status_query = "SELECT * FROM `online_users` WHERE `room` =     '{$rn}'";
 public function DisplayUsers(){
     $get_current_status = mysql_query($this->get_status_query);
     if(mysql_num_rows($get_current_status)!=0){
         while($row_status = mysql_fetch_array($get_current_status)){
             if($_SESSION['username']==true){
                     echo "<div class='online_margin'>   <b>".base64_decode($row_status['username'])."</b></div><hr style='border: 0; border-top:  solid 1px #D8D8D8;margin: 5px 10px 5px 10px;' />";
             }
         }
     }
 }
 }
 
 $Online = new WhosOnline;
 $Online->DisplayUsers();
 ?>
 

Any help?

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