Sending to a Multicast Group
You can send to a multicast socket using either a DatagramSocket or a MulticastSocket. What makes it multicast is the address that is in the datagram. If the address is a multicast address, the datagram will reach the multicast members in the group. You only need to use MulticastSocket if you want to control the time-to-live of the datagram. 

 byte[] outbuf = new byte[1024];
 int port = 1234;
 try {
   DatagramSocket socket = new DatagramSocket();
   InetAddress groupAddr = 
     InetAddress.getByName("228.1.2.3");
   DatagramPacket packet = 
     new DatagramPacket(outbuf, outbuf.length, 
       groupAddr, port);
   socket.send(packet);
 } catch (SocketException e) {
 } catch (IOException e) {
 }