A Group Chat Application in Java

import java.net.*; 
import java.io.*; 
import java.util.*; 
public class GroupChat 
{ 
    private static final String TERMINATE = "Exit"; 
    static String name; 
    static volatile boolean finished = false; 
    public static void main(String[] args) 
    { 
        if (args.length != 2) 
            System.out.println("Two arguments required: <multicast-host> <port-number>"); 
        else
        { 
            // CHANGES HAVE BEEN DONE HERE: Added validation for multicast address and port
            try
            { 
                InetAddress group = InetAddress.getByName(args[0]); 
                if (!group.isMulticastAddress()) {
                    System.out.println("Error: Invalid multicast address");
                    return;
                }
                
                int port = Integer.parseInt(args[1]); 
                if (port < 1024 || port > 65535) {
                    System.out.println("Error: Port number must be between 1024 and 65535");
                    return;
                }
                
                Scanner sc = new Scanner(System.in); 
                System.out.print("Enter your name: "); 
                name = sc.nextLine(); 
                
                MulticastSocket socket = new MulticastSocket(port); 
              
                // CHANGES HAVE BEEN DONE HERE: Set proper TTL value
                socket.setTimeToLive(1); // Changed from 0 to 1 for local subnet
                  
                socket.joinGroup(group); 
                Thread t = new Thread(new ReadThread(socket,group,port)); 
                t.start();  
                  
                System.out.println("Start typing messages...\n"); 
                try {
                    while(true) 
                    { 
                        String message = sc.nextLine(); 
                        if(message.equalsIgnoreCase(GroupChat.TERMINATE)) 
                        { 
                            finished = true; 
                            // CHANGES HAVE BEEN DONE HERE: Proper cleanup
                            socket.leaveGroup(group); 
                            socket.close(); 
                            sc.close(); // Added scanner close
                            break; 
                        } 
                        message = name + ": " + message; 
                        byte[] buffer = message.getBytes(); 
                        DatagramPacket datagram = new DatagramPacket(buffer,buffer.length,group,port); 
                        socket.send(datagram); 
                    } 
                } finally {
                    if (!socket.isClosed()) {
                        socket.leaveGroup(group);
                        socket.close();
                    }
                    sc.close();
                }
            } 
            catch(UnknownHostException uhe) {
                System.out.println("Error: Invalid multicast host");
                uhe.printStackTrace();
            }
            catch(NumberFormatException nfe) {
                System.out.println("Error: Port must be a number");
                nfe.printStackTrace();
            }
            catch(SocketException se) 
            { 
                System.out.println("Error creating socket"); 
                se.printStackTrace(); 
            } 
            catch(IOException ie) 
            { 
                System.out.println("Error reading/writing from/to socket"); 
                ie.printStackTrace(); 
            } 
        } 
    } 
} 

class ReadThread implements Runnable 
{ 
    private final MulticastSocket socket; // CHANGES HAVE BEEN DONE HERE: Made final
    private final InetAddress group; 
    private final int port; 
    private static final int MAX_LEN = 1000; 
    
    ReadThread(MulticastSocket socket, InetAddress group, int port) 
    { 
        this.socket = socket; 
        this.group = group; 
        this.port = port; 
    } 
      
    @Override
    public void run() 
    { 
        while(!GroupChat.finished) 
        { 
            byte[] buffer = new byte[ReadThread.MAX_LEN]; 
            DatagramPacket datagram = new DatagramPacket(buffer, buffer.length, group, port); 
            try
            { 
                socket.receive(datagram); 
                String message = new String(buffer, 0, datagram.getLength(), "UTF-8"); 
                if(!message.startsWith(GroupChat.name)) 
                    System.out.println(message); 
            } 
            catch(SocketException se) {
                if (!GroupChat.finished) {
                    System.out.println("Socket error: " + se.getMessage());
                }
            }
            catch(IOException e) 
            { 
                if (!GroupChat.finished) {
                    System.out.println("Error reading message: " + e.getMessage());
                }
            } 
        } 
    } 
}