class RecievePackets implements Runnable {
        String y = "";

        @Override
        public void run() {

            try {
                DatagramSocket socket = new DatagramSocket(port);
                socket.setReuseAddress(true);
                Log.e(TAG, "Bound to local port " + socket.getLocalPort());

                y = "";

                while (true)

                {

                    DatagramPacket packet = new DatagramPacket(new byte[256], 256);
                    socket.receive(packet);
                    InetAddress remote_addr = packet.getAddress();
                     ByteArrayInputStream bin = new ByteArrayInputStream(packet.getData());

                    for (int i = 0; i < packet.getLength(); i++) {
                        int data = bin.read();
                        if (data == -1)
                            break;
                        else {
                            y = y + (char) data;
                        }

                    }
                    list.addItem(y);  //problem is here
                    Log.e(TAG, "doInBackground: " + y);

                }
            } catch (Exception ioe) {
                Log.e(TAG, "Error - " + ioe);
            }
        }
}

@Override
    protected void onCreate(Bundle savedInstanceState) {

       Thread receive  = new Thread( new RecievePackets());
       receive.start();
}