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

public class myFirstTCPServer {
    public static void main(String[] args) throws IOException {

        int servPort = 4999;
        ServerSocket Sy = new ServerSocket(servPort);
        Socket servSocket = Sy.accept();

        InputStreamReader in = new InputStreamReader(servSocket.getInputStream());
        BufferedReader bf = new BufferedReader(in);
        String str = bf.readLine();

        while (!(str.equals("done"))){

            System.out.println("client connected");


            InetAddress address = InetAddress.getLocalHost();
            String ip = address.getHostAddress();
            System.out.println("IP: " + ip);
            System.out.println("Port: " + servPort);

            System.out.println("Message from client: " + str.toUpperCase());

            PrintWriter pr = new PrintWriter(servSocket.getOutputStream());
            pr.println(str);
            pr.flush();
        }
        servSocket.close();
    }
}

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

public class myFirstTCPClient {
    public static void main(String[] args) throws IOException {
        String S;
        Scanner input = new Scanner(System.in);
        System.out.println("Enter a sentence");
        S = input.nextLine();
        Socket clntSocket = new Socket(InetAddress.getLocalHost(), 4999);

        while (!(S.equals("done"))){
            double sent = System.nanoTime();
            PrintWriter pr = new PrintWriter(clntSocket.getOutputStream());
            pr.println(S);
            pr.flush();

            InputStreamReader in = new InputStreamReader(clntSocket.getInputStream());
            BufferedReader bf = new BufferedReader(in);

            String str = bf.readLine();
            System.out.println("Message from server: " + str);
            double received = System.nanoTime();
            double total = received - sent;
            System.out.println("Round Trip Time: " + (total/1000000.0));
        }
        clntSocket.close();
    }
}