public String getUsers(){
        StringBuffer ret = new StringBuffer(threads.size()*10+12);
        ret.append("Users in room: [");
        for (ChatServerThread thread : threads){
            if (thread!=null && thread.isLoggedIn() && thread.isAlive())
            ret.append(""+thread.getUserName()+", ");
        }
        ret.delete(ret.length()-2, ret.length());
        ret.append("]");
        return ret.toString();
    }