Example of using Multicast socket to exchange datagrams

gistfile1.java

import java.net.MulticastSocket;
import java.lang.Thread;
import java.net.InetAddress;
import java.net.DatagramPacket;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.net.UnknownHostException;

public class Client extends Thread {    

    private MulticastSocket sock;
    private InetAddress group;
    private int port;

    public Client(InetAddress group,int port) throws IOException {
        this.group = group;
        this.port = port;
        sock = new MulticastSocket(port);
        sock.setTimeToLive(2);
        sock.joinGroup(group);
    }  

    public void run(){
        System.out.println("Hi, I ("+this.getId()+") am listening!");
        try{
            while(true){
                DatagramPacket d = new DatagramPacket(new byte[256],256);
                sock.receive(d);
                String result = new String(d.getData());
                System.out.println(this.getId()+" received "+result);
            }
        }catch(IOException e){
            System.err.println("Arrrrgh: "+e);
        }
    } 

    public void send(String msg) throws IOException {
        byte[] data = msg.getBytes();
        System.out.println(this.getId() + " sending "+data);
        DatagramPacket d = new DatagramPacket(data,data.length,group,port);
        sock.send(d);
    }

    public static void main(String[] args){
        try{
            int n = Integer.parseInt(args[0]);
            Client[] clients = new Client[n];
            InetAddress group = InetAddress.getByName("224.255.255.255");
            for(int i=0; i<n;i++){
                int port = 9001;
                Client c = new Client(group,port);
                c.start();
                clients[i] = c;
            }
            BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
            while(true){
                String x = in.readLine();
                if(x=="exit"){ return; }
                clients[0].send(x); 
            }
        }catch(IOException e){ System.out.println("Argh: "+e); }
        /*catch(UnknownHostException e){ System.out.println("Zounds: "+e); }*/

    }
}