System.out.println("ERROR: XID in use !!!");
    public synchronized boolean send(DatagramPacket p, int id, SlpUdpCallback cb) throws ServiceLocationException {        if(callbackMap.containsKey(Integer.toString(id))) {            System.out.println("ERROR: XID in use !!!");            return false; // XID is in use !        }                // register XID and send message        callbackMap.put(Integer.toString(id), cb);        send(p);        return true;    }