Java MulticastSocket handle UDP client with thread

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket;

public class Main {
   static String name = "your name";
   static InetAddress addr;
   static int port = 3456;
   static MulticastSocket group;

   public static void main(String[] args) {

      try {//from  w  ww  . j a va2  s  . c  o  m
         addr = InetAddress.getByName("224.0.0.1");
         group = new MulticastSocket(port);
         new Receiver().start();
         new Sender().start();
      } catch (Exception e) {
         e.printStackTrace();
      }
   }

   static class Sender extends Thread {
      public void run() {
         try {
            BufferedReader fromUser = new BufferedReader(new InputStreamReader(System.in));
            while (true) {
               String msg = name + ":" + fromUser.readLine();
               byte[] out = msg.getBytes();
               DatagramPacket pkt = new DatagramPacket(out, out.length, addr, port);
               group.send(pkt);
            }
         } catch (Exception e) {
            e.printStackTrace();
         }
      }
   }

   static class Receiver extends Thread {
      public void run() {
         try {
            byte[] in = new byte[256];
            DatagramPacket pkt = new DatagramPacket(in, in.length);
            group.joinGroup(addr);
            while (true) {
               group.receive(pkt);
               System.out.println(new String(pkt.getData(), 0, pkt.getLength()));
            }
         } catch (Exception e) {
            e.printStackTrace();
         }
      }
   }
}