MiniChat.java

import java.net.*;
import java.util.*;

public class MiniChat {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        
        System.out.print("Your port: ");
        int myPort = sc.nextInt();
        System.out.print("Friend's port: ");
        int friendPort = sc.nextInt();
        sc.nextLine();
        
        DatagramSocket socket = new DatagramSocket(myPort);
        InetAddress friend = InetAddress.getByName("localhost");
        
        // Receiver thread
        new Thread(() -> {
            try {
                byte[] buf = new byte[1024];
                while (true) {
                    DatagramPacket p = new DatagramPacket(buf, buf.length);
                    socket.receive(p);
                    System.out.println("\nFriend: " + new String(p.getData(), 0, p.getLength()));
                    System.out.print("You: ");
                }
            } catch (Exception e) {}
        }).start();
        
        // Sender
        while (true) {
            System.out.print("You: ");
            String msg = sc.nextLine();
            byte[] data = msg.getBytes();
            socket.send(new DatagramPacket(data, data.length, friend, friendPort));
        }
    }
}