EchoClient.java

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

public class EchoClient {
    public static void main(String[] args) throws IOException {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Connecting to server ...");
        Socket sock = new Socket("localhost", 12345);
        DataInputStream in = new DataInputStream(sock.getInputStream());
        DataOutputStream out = new DataOutputStream(sock.getOutputStream());
        System.out.println("Connected.");

        int i = scanner.nextInt();
        out.writeInt(i);

        int result = in.readInt();
        System.out.println(result);
    }
}

EchoServer.java

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

public class EchoServer {
    public static void main(String[] args) {
        try {
            ServerSocket serverSock = new ServerSocket(12345);
            while (true) {
                Socket conn = serverSock.accept();
                new ClientThread(conn).start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

class ClientThread extends Thread {
    private Socket sock;

    public ClientThread(Socket sock) {
        this.sock = sock;
    }

    public void run() {
        try {
            DataInputStream in = new DataInputStream(sock.getInputStream());
            DataOutputStream out = new DataOutputStream(sock.getOutputStream());

            int number = (int) Math.floor(Math.random() * 100);
            int failedAttempts = 0;
            while (true) {
                if (failedAttempts >= 5) {
                    break;
                }

                int input = in.readInt();
                if (input > number) {
                    out.writeUTF("your number is too big");
                    failedAttempts += 1;
                } else if (input < number) {
                    out.writeUTF("your number is too small");
                    failedAttempts += 1;
                } else {
                    break;
                }
            }

            if (failedAttempts < 5) {
                out.writeUTF("yes, you have got the right number");
            } else {
                out.writeUTF("Sorry you have failed 5 times");
            }

            in.close();
            out.close();
            sock.close();
        } catch (EOFException e) {

        } catch (IOException e) {

        }
    }

    public static int factorial(int n) {
        if (n == 0) {
            return 1;
        } else {
            return n * factorial(n - 1);
        }
    }
}