Trouble writing a blocking method when asking GUI for input

Question

Hi,
I think this is more of a thread question than a GUI question, so that is why i posted it here...
My problem is I have a client/server application, and the client also has a GUI, which I get an input string from.
My problem is, that I don't know how to write a blocking method, which will wait for the GUI's input.
The example I provided below is very simple, and the obvious solution would be to use a JOptionPane, but that is not a viable solution. The way I am getting around this now is using a Thread.sleep call in my GUI, but I feel that this is incorrect, and there should be another way around it.
Here is my server class (w/ main method)
import java.net.*;
import java.io.*;
public class Server {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket(4444);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 4444.");
            System.exit(1);
        Socket clientSocket = null;
        try {
            clientSocket = serverSocket.accept();
        } catch (IOException e) {
            System.err.println("Accept failed.");
            System.exit(1);
        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        String  outputLine;
        outputLine = "Temp String";
        out.println(outputLine);
         System.err.println("Client: " + in.readLine());
        outputLine = "Bye";
        out.println(outputLine);
        out.close();
        in.close();
        clientSocket.close();
        serverSocket.close();
}Here is my client class (w/ main method)
import java.io.*;
import java.net.*;
public class Client {
    public static void main(String[] args) throws IOException {
        Socket kkSocket = null;
        PrintWriter out = null;
        BufferedReader in = null;
        try {
            kkSocket = new Socket("localhost", 4444);
            out = new PrintWriter(kkSocket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(kkSocket.getInputStream()));
        } catch (UnknownHostException e) {
            System.err.println("Don't know about host: localhost.");
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Couldn't get I/O for the connection to: localhost.");
            System.exit(1);
        ClientGUI cg = new ClientGUI();
        String fromServer;
        String fromUser;
        while ((fromServer = in.readLine()) != null) {
            System.out.println("Server: " + fromServer);
            if (fromServer.equals("Bye."))
                break;
            fromUser = cg.getInput();
         if (fromUser != null) {
                System.out.println("Client: " + fromUser);
                out.println(fromUser);
        out.close();
        in.close();
        kkSocket.close();
         System.exit(0);
}and here is the ClientGUI class (note: you need to resize it in order to see the textbox....
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class ClientGUI extends JFrame {
     private JTextField textBox = new JTextField();
     private JButton input = new JButton("Submit");
     private boolean recievedInput = false;
     private String inputText = "";
     public ClientGUI() {
          this.setupGUI();
     private ActionListener buttonAction = new ActionListener() {
          public void actionPerformed(ActionEvent e)  {
               inputText = textBox.getText();
               recievedInput = true;
     public String getInput() {
          while(recievedInput == false) {
               try {
                    Thread.sleep(2000);  //I  DONT want to do this!!
               catch(InterruptedException e) {
                    e.printStackTrace();
          recievedInput = false;
          return inputText;
     private void setupGUI() {
          textBox.setMinimumSize(new Dimension(100, 20));
          input.addActionListener(buttonAction);
          this.getContentPane().setLayout(new BorderLayout());
          this.getContentPane().add(textBox, BorderLayout.WEST);
          this.getContentPane().add(input, BorderLayout.EAST);
          this.pack();
          this.setSize(100,300);
          this.setVisible(true);
}If you have any ideas, I would greatly appreciate it

Answer 1

warnerja,
I tried the following, but I got an exception.
in the while loop inside Client.java, I put the following:
             synchronized(cg) {
                  try {
                      cg.wait();
                    fromUser = cg.getInput();
                  catch(InterruptedException e) {
                       e.printStackTrace();
             }and inside my ClientGUI class, I put the following:
private ActionListener buttonAction = new ActionListener() {
          public void actionPerformed(ActionEvent e)  {
               inputText = textBox.getText();
               ClientGUI.this.notify();
     public String getInput() {
          return inputText;
     }But I got this exception:
Exception in thread "AWT-EventQueue-0" java.lang.IllegalMonitorStateException: current thread not owner
     at java.lang.Object.notify(Native Method)
     at ClientGUI$1.actionPerformed(ClientGUI.java:21)
any idea what I am doing wrong?