log.error("MyReceiver: problem sending response to " + sender);
System.err.println("MyReceiver: problem sending response to " + sender);
        public void receive(DatagramPacket packet) {            System.out.println("-- received " + packet.getLength() + " bytes from " + packet.getSocketAddress());            InetAddress sender=packet.getAddress();            byte[] buf=packet.getData();            int len=packet.getLength();            String tmp=new String(buf, 0, len);            if(len > 4) {                if(tmp.startsWith("rsp:")) {                    System.out.println("-- received respose: \"" + tmp + '\"');                    return;                }            }            byte[] rsp_buf=("rsp: this is a response to " + tmp).getBytes();            DatagramPacket response=new DatagramPacket(rsp_buf, rsp_buf.length, sender, packet.getPort());            try {                t.send(response);            }            catch(Exception e) {                e.printStackTrace();                log.error("MyReceiver: problem sending response to " + sender);            }        }