// Purpose.  Sending and receiving UDP datagrams

import java.io.*;
import java.net.*;

class UDPsend extends Thread {
   public void run() {
      try {
         DatagramSocket socket = new DatagramSocket();
         DatagramPacket packet;
         String str;
         for (int i=1; i < 6; i++) {
            str = "message " + i;
            System.out.println( "sending --" + str + "--" );
            packet = new DatagramPacket( str.getBytes(),
               str.length(), InetAddress.getByName("127.0.0.1"), 8189 );
            socket.send( packet );
            Thread.sleep( 50 );
         }
         socket.close();
      } catch( Exception e ) { e.printStackTrace(); }
}  }

class UDPreceive extends Thread {
   public void run() {
      try {
         DatagramSocket socket = new DatagramSocket( 8189 );
         DatagramPacket packet;
         byte[] buf = new byte[30];
         String str;
         for (int i=1; i < 6; i++) {
            packet = new DatagramPacket( buf, buf.length );
            socket.receive( packet );
            str = new String( buf, 0, packet.getLength() );
            System.out.println( "   receiving --" + str + "--" );
         }
         socket.close();
      } catch( IOException e ) { e.printStackTrace(); }
}  }

public class UDPdemo {
   public static void main( String[] args ) {
      new UDPsend().start();
      new UDPreceive().start();
}  }

// sending --message 1--
//    receiving --message 1--
// sending --message 2--
//    receiving --message 2--
// sending --message 3--
//    receiving --message 3--
// sending --message 4--
//    receiving --message 4--
// sending --message 5--
//    receiving --message 5--