concurrent client server TCP

import java.io.*;
import java.nio.*;
import java.net.*;
class ComplexTCPServer extends Thread
{
    Socket connectionSocket;
    ComplexTCPServer(Socket c)
    {
        connectionSocket=c;
        this.start();
    }
    public void run()
    {
        String clientSentence;
        String capitalizedSentence;
        System.out.println("Client Connected");
        try
        {
            BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
            PrintWriter outToClient = new PrintWriter(connectionSocket.getOutputStream());
            clientSentence = inFromClient.readLine();
            System.out.println("Received: " + clientSentence);
            capitalizedSentence = clientSentence.toUpperCase() + '\n';
            outToClient.println(capitalizedSentence);
            outToClient.close();
            inFromClient.close();
        }
        catch(IOException e)
        {

        }

    }
    public static void main(String argv[]) throws Exception
    {
        ServerSocket welcomeSocket = new ServerSocket(6789);
        System.out.println("Server waiting for Clients");
        while(true)
        {
            new ComplexTCPServer(welcomeSocket.accept());
        }
    }
}

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

import java.io.*;
import java.net.*;
class SimpleTCPClient
{
    public static void main(String argv[]) throws Exception
    {
        String sentence;
        String modifiedSentence;

        BufferedReader inFromUser = new BufferedReader( new InputStreamReader(System.in));
        Socket clientSocket = new Socket("127.0.0.1", 6789);
        System.out.println("Client Connected with Server");

        PrintWriter outToServer = new PrintWriter(clientSocket.getOutputStream(),true);
        BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        System.out.print("Enter A Message ");
        sentence = inFromUser.readLine();
        outToServer.println(sentence);
        System.out.println("Message Sent to Server");

        modifiedSentence = inFromServer.readLine();
        System.out.println("Message Received from Server");
        System.out.println("FROM SERVER: " + modifiedSentence);

        inFromUser.close();
        outToServer.close();
        inFromServer.close();
        clientSocket.close();
    }
}