Client/server program: Urgent, pls help!!

Question

I am new to Java, particularly Networking in Java, while writing client/server application I have got completely strucked now. Can any one give me an idea where I am wrong?
I am writing a simple client server application in Java using Socket and ServerSocket classes as a part of my course work. Through client I am just establishing connection with server, getting user inputs/commands, sending the same input to server (server will capitalize this input and return it back to client), receiving and displaying server�s response.
The connection is established fine. Even it is accepting users input well but I am getting runtime NullPointerException while trying to send it to server. Here is the working of my client command window.
C:\Program Files\j2sdk_nb\j2sdk1.4.2\bin\abc>javac TClient.java
C:\Program Files\j2sdk_nb\j2sdk1.4.2\bin\abc>java TClient
Enter the message
hello
Exception in thread "main" java.lang.NullPointerException
at TClient.Send_Message(TClient.java:46)
at TClient.main(TClient.java:76)
C:\Program Files\j2sdk_nb\j2sdk1.4.2\bin\abc>
As soon as I get this exception the connection with server is lost and I get this in server command window.
C:\Program Files\j2sdk_nb\j2sdk1.4.2\bin\abc>javac TCPServer.java
C:\Program Files\j2sdk_nb\j2sdk1.4.2\bin\abc>java TCPServer
Exception in thread "main" java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(SocketInputStream.java:168)
at java.io.ObjectInputStream$PeekInputStream.read(ObjectInputStream.java
:2150)
at java.io.ObjectInputStream$PeekInputStream.readFully(ObjectInputStream
.java:2163)
at java.io.ObjectInputStream$BlockDataInputStream.readShort(ObjectInputS
tream.java:2631)
at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:734
at java.io.ObjectInputStream.<init>(ObjectInputStream.java:253)
at TCPServer.main(TCPServer.java:17)
C:\Program Files\j2sdk_nb\j2sdk1.4.2\bin\abc>
Here is my code for server (TCPServer.java)
import java.io.*;
import java.net.*;
class TCPServer {
  public static void main(String argv[]) throws Exception
      String clientSentence;
      String capitalizedSentence;
      ServerSocket welcomeSocket = new ServerSocket(80);
      while(true) {
                   Socket connectionSocket = welcomeSocket.accept();
           ObjectInputStream inFromClient =  new ObjectInputStream(connectionSocket.getInputStream());
           ObjectOutputStream  outToClient =
             new ObjectOutputStream(connectionSocket.getOutputStream());
           clientSentence = (String ) inFromClient.readObject();
           capitalizedSentence = clientSentence.toUpperCase() + '\n';
           outToClient.writeObject(capitalizedSentence);
And this is for Client (TClient.java)
import java.io.*;
import java.net.*;
import java.util.*;
class TClient {
     private ObjectOutputStream  server_output;
            private ObjectInputStream server_input;
     private Socket client;
     private void server_connect() throws IOException
          client = new Socket(InetAddress.getLocalHost(), 80);
     private void getstreams() throws IOException
      server_output = new ObjectOutputStream (client.getOutputStream());
      server_output.flush();     
         server_input = new ObjectInputStream(client.getInputStream());
     private String get_cmd_frm_usr() throws IOException
          BufferedReader inFromUser =
                     new BufferedReader(new InputStreamReader(System.in));
          String sentence;
          System.out.println("Enter the message");
          sentence = inFromUser.readLine();
          /*StringTokenizer st = new StringTokenizer(sentence);
               while (st.hasMoreTokens()) //separating n printing words of inputted sentence
                   System.out.println(st.nextToken());
     return(sentence);
     private void Send_Message(String msg) throws IOException
          //System.out.println("within send_message method :"+ msg);
          server_output.writeObject( msg );
          server_output.flush();
     private void recieve_n_disp_mess() throws Exception
     String modifiedSentence;
     modifiedSentence = ( String ) server_input.readObject();
     System.out.println("\n\n  by SERVER: " +      modifiedSentence);
        private void close_connection() throws IOException
          client.close();
     public static void main(String args[]) throws Exception
          TClient client = new TClient();
         try{
          client.server_connect();
          String command=client.get_cmd_frm_usr();
          //System.out.println("this is returned from input method n ready to sent to server soon: "+ command);
          client.Send_Message(command);
          client.recieve_n_disp_mess();
          client.close_connection();
               } catch(EOFException eofException) {}
          catch (IOException ioException) {}          

Answer 1

you never initialized the server_output and the server_input vriables...
I see you have the getstreams() function which should initialize them but you never call it...
so untill you will call it those variables will stay null.
I can also see you do not implement constructors, its much easier just to implement these instead of functions initializing variables...
Hope it will help
private void getstreams() throws IOException
server_output = new ObjectOutputStream
(client.getOutputStream());
server_output.flush();
server_input = new
ObjectInputStream(client.getInputStream());
public static void main(String args[]) throws
Exception
TClient client = new TClient();
try{
client.server_connect();
String command=client.get_cmd_frm_usr();
//System.out.println("this is returned from input method n ready to sent to server soon: "+ command);
client.Send_Message(command);
client.recieve_n_disp_mess();
client.close_connection();
} catch(EOFException eofException) {}
catch (IOException ioException) {}