Server.java

import java.net.*;
import java.io.*;

public class Server {

    ServerSocket server;
    Socket socket;
    BufferedReader br;
    PrintWriter out;

    // CONSTRUCTOR
    public Server() {

        try {
            server = new ServerSocket(7777);
            System.out.println("server is ready to accept connection");
            System.out.println("waiting......");
            socket = server.accept();

            br = new BufferedReader(new InputStreamReader(socket.getInputStream()));

            out = new PrintWriter(socket.getOutputStream());

            startReading();
            startWriting();

        } catch (Exception e) {
            e.getStackTrace();
        }

    }

    public void startReading() {
        Runnable r1 = () -> {
            System.out.println("reader started");
            try {
                while (true) {

                    String msg = br.readLine();

                    if (msg.equals("exit")) {
                        System.out.println("chat is terminated by Client");
                        socket.close();
                        break;
                    }
                    System.out.println("Client:" + msg);
                }
            } catch (Exception e) {
                e.getStackTrace();
            }

        };
        new Thread(r1).start();
    }

    public void startWriting() {
        Runnable r2 = () -> {
            System.out.println("writer started");
            try {
                while (!socket.isClosed()) {

                    BufferedReader br1 = new BufferedReader(new InputStreamReader(System.in));
                    String content = br1.readLine();

                    out.println(content);
                    out.flush();

                    if (content.equals("exit")) {
                        socket.close();
                        break;
                    }

                }
            } catch (Exception e) {
                e.getStackTrace();
            }

        };
        new Thread(r2).start();
    }

    public static void main(String[] args) {
        System.out.println("going to start server");
        new Server();
    }
}