//Importing the required classes.
import java.io.*;
import java.net.*;

class TCPServer {
   public static void main(String argv[]) throws Exception
      {
         String clientSentence;//Variable to store characters received from client.
         String capitalizedSentence;//Variable to store the capitalized characters to be sent to client.

         //Instantiation of socket object on the server. Port number is 6789.
         ServerSocket welcomeSocket = new ServerSocket(6789);

		 //Server continuously listens for requests from clients.
         while(true) {
			//Waiting for a request from client and instantiating a connection between server and client.
            Socket connectionSocket = welcomeSocket.accept();

            //Instantiating BufferedReader and InputStreamReader classes to read strings from client.
            BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));

            //Instatiating object to send data back to client.
            DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());

			//Reading a line from client and storing it in the variable.
            clientSentence = inFromClient.readLine();

            //Capitalizing the data read from client.
            capitalizedSentence = clientSentence.toUpperCase() + '\n';

            //Displaying the client data on the server console.
            System.out.println(clientSentence);

            //Writing back the capitalized sentence back to client.
            outToClient.writeBytes(capitalizedSentence);


			//Closing the client reader.
            inFromClient.close();

            //Closing the client writer.
            outToClient.close();

            //Closing the connection.
            connectionSocket.close();
         }
      }
}