※ Multicast IP Address를 이용한 chatting  
     Multicast Ip address를 이요한 채팅 프로그램입니다. 
 import java.io.*;
 import java.net.*;
 import java.awt.*;
 import java.awt.event.*;

 public class Multicast implements Runnable, ActionListener {
private Frame f;
private TextField tf;
private TextArea ta;

private InetAddress group;
private MulticastSocket s;

public Multicast() {
	f = new Frame("MulticatSocket Example");
	tf = new TextField();
	ta = new TextArea();

	f.addWindowListener(new WindowAdapter() {
		public void windowClosing(WindowEvent e) {
			try {
				s.leaveGroup(group);
			} catch(IOException ex) {
				ex.printStackTrace();
			}
			System.exit(0);
		}
	});
	tf.addActionListener(this);
	f.add(ta);
	f.add(tf,"South");
	f.setSize(300,400);
	f.setVisible(true);
	
	try	{
		group = InetAddress.getByName("228.5.6.7");
		s = new MulticastSocket(6789);
		s.joinGroup(group);
	}catch (Exception e){
		e.printStackTrace();
	}		
}

public static void main(String args[]) {
	Multicast cast = new Multicast();
	Thread t = new Thread(cast);
	t.start();
}

public void actionPerformed(ActionEvent e) {
	String msg = tf.getText();
	System.out.println("send data : "+msg);
	DatagramPacket hi = new DatagramPacket(
	  msg.getBytes(), msg.getBytes().length,group, 6789
	);
	try	{
		s.send(hi);
	}catch (IOException ex){
		ex.printStackTrace();
	}
	tf.setText("");
}

public void run() {
try	{
	byte[] buf = new byte[1000];				
	while(true) {
		DatagramPacket recv = new DatagramPacket(buf, buf.length);
		System.out.println("listen..");
		s.receive(recv);
		String data = new String(recv.getData(),0,recv.getLength());
		System.out.println("receive data : "+data);
		InetAddress inet = recv.getAddress();
		ta.append(inet.getHostAddress()+"] "+data+"\n");
	}
}catch (Exception e){
	e.printStackTrace();
}
}
 }
 ▶ Multicast.java 

 
2001.05.17 written by Jeon HongSeong