Client.java

import java.io.*;
import java.net.Socket;
import java.util.Scanner;

public class Client {
    private Socket socket;
    private BufferedReader bufferedReader;
    private BufferedWriter bufferedWriter;
    private String username;

    public Client(Socket socket, String username) {
        try {
            this.socket = socket;
            this.bufferedWriter = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
            this.bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            this.username = username;
        } catch (IOException e) {
            closeEverything(socket, bufferedReader, bufferedWriter);
        }
    }

    // METHOD 1: Send messages (Runs on the Main Thread)
    public void sendMessage() {
        try {
            // 1. Send username first
            bufferedWriter.write(username);
            bufferedWriter.newLine();
            bufferedWriter.flush();

            Scanner scanner = new Scanner(System.in);

            // 2. Keep sending messages
            while (socket.isConnected()) {
                String messageToSend = scanner.nextLine();
                bufferedWriter.write(username + ": " + messageToSend);
                bufferedWriter.newLine();
                bufferedWriter.flush();
            }
        } catch (IOException e) {
            closeEverything(socket, bufferedReader, bufferedWriter);
        }
    }

    // METHOD 2: Listen for messages (Runs on a Background Thread)
    public void listenForMessage() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                String msgFromGroupChat;
                while (socket.isConnected()) {
                    try {
                        // This line pauses until a message arrives
                        msgFromGroupChat = bufferedReader.readLine();
                        System.out.println(msgFromGroupChat);
                    } catch (IOException e) {
                        closeEverything(socket, bufferedReader, bufferedWriter);
                    }
                }
            }
        }).start(); // Start the thread immediately
    }

    public void closeEverything(Socket socket, BufferedReader bufferedReader, BufferedWriter bufferedWriter) {
        try {
            if (bufferedReader != null) bufferedReader.close();
            if (bufferedWriter != null) bufferedWriter.close();
            if (socket != null) socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) throws IOException {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter your username for the group chat: ");
        String username = scanner.nextLine();

        Socket socket = new Socket("localhost", 1234);
        Client client = new Client(socket, username);

        // Start the background listener
        client.listenForMessage();

        // Start the sender (this blocks the main thread)
        client.sendMessage();
    }
}