import java.io.*;
import java.net.*;


/**
 * demonstrates how to write datagram server
 *
 * @see datagramclientdemo
 ***/
public class datagramserverdemo
{
    public static void main(string args[]) throws exception
    {
        byte data[] = new byte[20];

        // client on port 4444, server on 5555
        datagramsocket socket = new datagramsocket(5555);
        datagrampacket packet = new datagrampacket(data, 20);

        socket.receive(packet);
        string received = new string(packet.getdata(), 0);
        system.out.println(received);

        string sendmsg="hello back";
        sendmsg.getbytes(0, sendmsg.length(), data, 0);
        packet  = new datagrampacket(data, 20,
                                packet.getaddress(),
                                packet.getport());
        socket.send(packet);
    }
}