URGENT : java exception

Question

hello
I have a quiz system that has a server, a player and a friend client. I have tried running them( by directly running their main classes) it works fine.
However when i load a player and a friend client from a main interface by clicling on their respective jButton, the respective interfaces are loaded but i get the following error:
Exception in thread "Thread-3" java.lang.NullPointerException
at playerQuiz.src.QuizClient.run(QuizClient.java:318)
at java.lang.Thread.run(Thread.java:595)
But as i have already mentioned the program works perfectly when not loaded from a button.
can someone please help.
Edited by: ojm22 on Jun 8, 2008 2:21 AM

Answer 1

The class QuizClient :
package playerQuiz.src;
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.net.*;
import java.io.*;
import java.util.*;
public class QuizClient extends JFrame implements ActionListener, Runnable {
    String moneySum[] = {"5", "10", "20", "30", "40", "45", "50", "55",
                         "60", "70", "75", "80",
                         "85", "90", "95", "100 "};
    static PrintStream out;         // for sending to server.
    static BufferedReader in;       // for getting data from server.
    // socket for connection with the server:
    static Socket socket = null;
    // label to show status messages:
    JLabel lblStatus = new JLabel("Connected! Waiting for a friend...", JLabel.CENTER);
    // label to show questions:
    JLabel lblQuestion = new JLabel(" ", JLabel.CENTER);
    // label to just to show "wheels" label:
    JLabel lblWheels = new JLabel("  Wheels");
    // label to show how many friend wheels are left:
    JLabel lblFriend = new JLabel("  Friend:   ?");
    // label to show how many 50:50 wheels are left:
    JLabel lbl5050 = new JLabel("  50:50 :   ?");
    // label to show how many wheels of the public are left:
    JLabel lblThePublic = new JLabel("  Public:   ?");
    // answer boxes for possible answers:
    AnswerBox cbAnswers[] = new AnswerBox[4];
    // buttons:
    JButton btnFinal, btnFriend, btn5050, btnThePublic, btnRetire;
    // money boxes:
    PointBox cbMoney[] = new PointBox[15];
    // response chart for the public:
    Chart publicChart = new Chart();
    int selectedAnswer = -1; // last clicked answer.
    int moneyIndex = 0;    // money index, updated by server.
    // will be true when friend will also be connected:
    public boolean ALL_CONNECTED = false;
    // thread which cares about receiving data from server:
    Thread thServer = null;
    * Default Constructor.
    public QuizClient()
        super ("The Revision Quiz");
        // look & feel setup:
        try {
            UIManager.setLookAndFeel(
                UIManager.getSystemLookAndFeelClassName() );
        } catch (Exception e) {
            System.err.println("Couldn't use the system "
                             + "look and feel: " + e);
        // update look & feel for those components created in
        //     declaration (if required):
        lblStatus.updateUI();
        lblQuestion.updateUI();
        lblWheels.updateUI();
        lblFriend.updateUI();
        lbl5050.updateUI();
        lblThePublic.updateUI();
        // processing window events:
        WindowListener L= new WindowAdapter () {
            public void windowClosing(WindowEvent e) {
                closeApplication();
        addWindowListener(L);
        // prepare the layout:
        JPanel  pMain = new JPanel ();
        pMain.setLayout(new BorderLayout());
        JPanel pUpper = new JPanel();           // for labels.
        pUpper.setLayout(new GridLayout(2,1));
        JPanel  pCenter = new JPanel ();        // for answers.
        pCenter.setLayout(new BorderLayout());
        JPanel pAnswers = new JPanel();           // for answers & the public chart.
        pAnswers.setLayout(new GridLayout(2,2, 20,20));
        // for buttons:
        JPanel pButtons = new JPanel(new FlowLayout(FlowLayout.CENTER,10,10));
        JPanel pLeft = new JPanel(new GridLayout(15,1, 10,10));  // for wheels counters.
        JPanel pRight = new JPanel(new GridLayout(15,1, 1,1));   // for money boxes.
        pUpper.add(lblStatus);
        pUpper.add(lblQuestion);
        pLeft.add(lblWheels);
        pLeft.add(lblFriend);
        pLeft.add(lbl5050);
        pLeft.add(lblThePublic);
        // make & add check boxes for answers:
        cbAnswers[0] = new AnswerBox ("A:",pAnswers);   // first possible answer.
        pAnswers.add(cbAnswers[0]);
        cbAnswers[0].addActionListener(this);
        cbAnswers[1] = new AnswerBox ("B:",pAnswers);   // second possible answer.
        pAnswers.add(cbAnswers[1]);
        cbAnswers[1].addActionListener(this);
        cbAnswers[2] = new AnswerBox ("C:",pAnswers);   // third possible answer.
        pAnswers.add(cbAnswers[2]);
        cbAnswers[2].addActionListener(this);
        cbAnswers[3] = new AnswerBox ("D:",pAnswers);   // fourth possible answer.
        pAnswers.add(cbAnswers[3]);
        cbAnswers[3].addActionListener(this);
        // make & add buttons:
        btnFinal = new JButton("Final");        // for confirmation of answer.
        pButtons.add(btnFinal);
        btnFinal.addActionListener(this);
        btnFriend = new JButton("Friend");      // for friend request.
        pButtons.add(btnFriend);
        btnFriend.addActionListener(this);
        btn5050 = new JButton("50:50");         // for 50:50 request.
        pButtons.add(btn5050);
        btn5050.addActionListener(this);
        btnThePublic = new JButton("The Public");   // for request of the public.
        pButtons.add(btnThePublic);
        btnThePublic.addActionListener(this);
        btnRetire = new JButton("Retire");      // for request to retire.
        pButtons.add(btnRetire);
        btnRetire.addActionListener(this);
        enableButtons(false);     // disable all buttons.
        // make money boxes:
        for (int i=14; i>=0; i--) {
            cbMoney[i] = new PointBox (moneySum[i+1], pRight);
            pRight.add(cbMoney);
cbMoney[4].setStopStation(); // "1,000"
cbMoney[9].setStopStation(); // "32,000"
pCenter.add (pAnswers, BorderLayout.SOUTH);
// add response chart for the public:
publicChart.setVisible(false); // shown only when required.
pCenter.add (publicChart, BorderLayout.CENTER);
// Add sub layouts to main layout:
pMain.add(pUpper, BorderLayout.NORTH);
pMain.add(pButtons, BorderLayout.SOUTH);
pMain.add(pCenter, BorderLayout.CENTER);
pMain.add(pLeft, BorderLayout.WEST);
pMain.add(pRight, BorderLayout.EAST);
// -------- set colors and fonts:
pButtons.setBackground(Color.lightGray );
pAnswers.setBackground(Color.lightGray );
pCenter.setBackground(Color.lightGray );
pUpper.setBackground(Color.lightGray );
pRight.setBackground(Color.lightGray) ;
pLeft.setBackground(Color.lightGray);
lblStatus.setForeground(Color.yellow);
lblQuestion.setForeground(Color.black);
lblWheels.setForeground(Color.green);
lblFriend.setForeground(Color.white);
lbl5050.setForeground(Color.white);
lblThePublic.setForeground(Color.white);
Font f1 = new Font("Arial", Font.BOLD, 12);
Font f2 = new Font("Arial", Font.BOLD, 20);
lblStatus.setFont(f1);
lblQuestion.setFont(f2);
lblWheels.setFont(f1);
lblFriend.setFont(f1);
lbl5050.setFont(f1);
lblThePublic.setFont(f1);
// show the window:
setContentPane (pMain);
setSize(590,450);
setVisible(true);
// start the thread that cares about receiving data from server:
thServer = new Thread (this);
thServer.start();
* Main function, from where QuizClient starts.
public static void main(String args[]) {
     String serverAddress = "172.22.45.120";
     int serverPort = 4450;
     try {
               socket = new Socket(serverAddress, serverPort);
          } catch (UnknownHostException e1) {
               // TODO Auto-generated catch block
               e1.printStackTrace();
          } catch (IOException e1) {
               // TODO Auto-generated catch block
               e1.printStackTrace();
System.out.println(socket);
// open in and out streams for talking with the server:
try {
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
out = new PrintStream(socket.getOutputStream());
catch (IOException e) {
System.err.println("Open streams -> " + e);
System.exit(1);
// print the address of player - for verification:
InetAddress localHost = null;
try {
localHost = InetAddress.getLocalHost();
} catch (UnknownHostException e) {
System.out.println("Unknown host - probably localhost with no IP!");
// no exit, since can work on "localhost" without internet.
System.out.println("Player's local address: " + localHost);
// create QuizClient and show its window:
new QuizClient();
private void pause(int time) {
try {
Thread.sleep(time);
catch (InterruptedException e) {
System.err.println(e.getMessage());
* The run method of that is used by a thread.
public void run() {
Thread thisThread = Thread.currentThread();
// thread which cares about receiving data from server:
while (thServer == thisThread) {
String serverInput;
try {
if ((serverInput = in.readLine()) != null)
gotMessageFromServer(serverInput); // trigger "event".
catch (IOException ioe) {
JOptionPane.showMessageDialog(this,
ioe + "\nNot regular game termination!",
"Cannot read from server!",
JOptionPane.ERROR_MESSAGE);
closeApplication(); // force to close.
} // end of run().
public void actionPerformed(ActionEvent e){
Object src=e.getSource();
if (src == btnFinal) {            // confirmation of answer.
if (selectedAnswer != -1) {
enableButtons(false); // disable all buttons.
lblStatus.setText("Waiting for server's response...");
sendToServer("FINAL:" + selectedAnswer);
else {
JOptionPane.showMessageDialog(this,
"Please select an answer!",
"Not selected!", JOptionPane.ERROR_MESSAGE);
else if (src == btnFriend) {     // friend request.
enableButtons(false); // disable all buttons.
lblStatus.setText("Waiting for friend's response...");
sendToServer("FRIEND");
else if (src == btn5050) {        // 50:50 request.
enableButtons(false); // disable all buttons.
lblStatus.setText("Waiting for server's response...");
sendToServer("50:50");
else if (src == btnThePublic) {   // request of the public.
enableButtons(false); // disable all buttons.
publicChart.setChart(0, 0, 0, 0); // reset the chart from any data.
publicChart.setVisible(true); // show the chart.
lblStatus.setText("Waiting for server's response...");
sendToServer("THE_PUBLIC");
else if (src == btnRetire) {     // request to retire.
enableButtons(false); // disable all buttons.
lblStatus.setText("Waiting for server's response...");
sendToServer("RETIRE");
else{
// clicks on check-boxes:
for (int i=0; i<4; i++)
if (cbAnswers[i] == src) {  // click on one of the answer boxes.
selectedAnswer = i+1; // +1 because first is 1.
// deselect any other selected check-boxes
// except the last one:
for (int k=0; k<4; k++) {
if (k != i) // not equal to selected.
cbAnswers[k].setSelected(false);
else
cbAnswers[k].setSelected(true);
return; // no need to continue.
} // end of actionPerformed().
private void setMoney(String sm) {
int k;
try {
k = Integer.parseInt(sm);
catch(NumberFormatException e) {
System.err.println("setMoney()--> " + e);
return;
// validation (should be between 0 and 15):
if ((k > 15) || (k < 0)) {
System.err.println("setMoney() out of bounds --> " + sm);
return;
moneyIndex = k; // store in global variable.
updateEarnedMoney();
private void updateEarnedMoney() {
// select earned stations:
for (int i=0; i<moneyIndex; i++)
cbMoney[i].setSelected(true);
// clear all the others:
for (int i=moneyIndex; i<15; i++)
cbMoney[i].setSelected(false);
private void gotMessageFromServer(String msg) {
System.out.println("SERVER: [" + msg + "]");
if (msg.equals("ALL_CONNECTED")) {   // game started.
ALL_CONNECTED = true;
sendToServer("RESTART"); // reset everything.
sendToServer("QUESTION"); // ask for first question.
else if (msg.startsWith("Q:")) {    // question.
prepareForNextQuestion();
lblQuestion.setText(extractData(msg));
else if (msg.startsWith("A1:")) {       // first possible answer.
cbAnswers[0].setText(extractData(msg));
else if (msg.startsWith("A2:")) {       // second possible answer.
cbAnswers[1].setText(extractData(msg));
else if (msg.startsWith("A3:")) {       // third possible answer.
cbAnswers[2].setText(extractData(msg));
else if (msg.startsWith("A4:")) {       // fourth possible answer.
cbAnswers[3].setText(extractData(msg));
// got last possible answer, so enable buttons:
enableButtons(true);
lblStatus.setText(" "); // clear the status.
else if (msg.startsWith("MONEY:")) {    // earned money index.
setMoney(extractData(msg));
else if (msg.startsWith("FRIEND:")) {  // how many friend tips left.
lblFriend.setText (" Friend: " + extractData(msg));
else if (msg.startsWith("50_50:")) {  // how many 50:50 tips left.
lbl5050.setText (" 50:50 : " + extractData(msg));
else if (msg.startsWith("THE_PUBLIC:")) {  // how many tips of the public left.
lblThePublic.setText (" Public: " + extractData(msg));
else if (msg.equals("NOFRIEND!")) {     // error - no more friend tips!
lblStatus.setText(" "); // clear the status.
JOptionPane.showMessageDialog(this,
"Server says you have no more friend tips, sorry.",
"No more friend tips", JOptionPane.ERROR_MESSAGE);
enableButtons(true);
else if (msg.equals("NO50:50!")) {      // error - no more 50:50 tips!
lblStatus.setText(" "); // clear the status.
JOptionPane.showMessageDialog(this,
"Server says you have no more 50:50 tips, sorry.",
"No more 50:50 tips", JOptionPane.ERROR_MESSAGE);
enableButtons(true);
else if (msg.equals("50:50TWICE!")) {   // error - 50:50 done twice already!
lblStatus.setText(" "); // clear the status.
JOptionPane.showMessageDialog(this,
"Server says you have done 50:50 twice already for this question!",
"Cannot do 50:50 three times for one question", JOptionPane.ERROR_MESSAGE);
enableButtons(true);
else if (msg.equals("NO_PUBLIC!")) {    // error - no more tips of the public!
lblStatus.setText(" "); // clear the status.
JOptionPane.showMessageDialog(this,
"Server says you have no more tips of the public, sorry.",
"No more tips of the public!", JOptionPane.ERROR_MESSAGE);
enableButtons(true);
publicChart.setVisible(false); // hide the chart (it's empty).
else if (msg.startsWith("GREEN:")) {   // set right answer be green.
try { // generally, server sends the right data, check anyway
int k = Integer.parseInt(extractData(msg));
cbAnswers[k-1].setCorrect();
} catch (Exception e) {
System.out.println("GREEN: -> " + e);
else if (msg.equals("RIGHT!")) {      // last question was answered correctly!
lblStatus.setText(" "); // clear the status.
JOptionPane.showMessageDialog(this,
"This is the right answer!",
"Congratulations!", JOptionPane.INFORMATION_MESSAGE);
lblStatus.setText("Waiting for server's response...");
sendToServer("QUESTION"); // ask for next question.
else if (msg.equals("MILLION!")) {    // correct, and you won a million!
lblStatus.setText(" "); // clear the status.
JOptionPane.showMessageDialog(this,
"You passed with Distinction!",
"Congratulations! - Game over.", JOptionPane.INFORMATION_MESSAGE);
askToRestart();
else if (msg.startsWith("WRONG!:")) { // last question was answered WRONG!
lblStatus.setText(" "); // clear the status.
JOptionPane.showMessageDialog(this,
"Your answer is wrong!\n Correct answer is " +
indexToLetter( extractData(msg) ) +
"\nYour current marks is \t" + moneySum[moneyIndex],
"Game over!", JOptionPane.ERROR_MESSAGE);
askToRestart();
else if (msg.startsWith("RETIRED:")) { // retire request confirmed.
lblStatus.setText(" "); // clear the status.
JOptionPane.showMessageDialog(this,
"Your current marks is" + moneySum[moneyIndex] + ",\n" +
"and the right answer for the last question is " +
indexToLetter ( extractData(msg) ),
"Retired!", JOptionPane.INFORMATION_MESSAGE);
askToRestart();
else if (msg.startsWith("FRIEND_ANSWER:")) {    // getting friend answer.
lblStatus.setText("Your friend thinks answer is: " +
indexToLetter( extractData(msg) ) );
// got answer from friend, so enable the buttons:
enableButtons(true);
else if (msg.equals("FRIEND_DONTKNOW")) {       // friend doesn't know!
lblStatus.setText("Your friend doesn't know the answer...");
// friend says he doesn't know, so enable the buttons:
enableButtons(true);
else if (msg.equals("FRIEND_TIMEUP")) {         // friend's time is up!
lblStatus.setText("Your friend failed to give answer in 30 seconds...");
// time is up, so enable the buttons:
enableButtons(true);
else if (msg.startsWith("TIMER:")) {            // timer state for friend.
lblStatus.setText("Your friend has: " + extractData(msg) + " seconds.");
else if (msg.startsWith("Message from Server:")) {
lblStatus.setText(msg);
else if (msg.equals("FRIEND_DISCONECTED")) {    // error - friend disconected.
// though the game can be continued without the friend,
// we decided to end the game to avoid processing the state
// when friend is required and it's not there....
lblStatus.setText(" "); // clear the status.
JOptionPane.showMessageDialog(this,
"Your Friend has disconnected!\n" +
"Server terminated the game.",
"Friend disconnected!",
JOptionPane.ERROR_MESSAGE);
closeApplication(); // force to close.
else if (msg.equals("WATING_PREV_FRIEND")) {    // error - server not ready!
lblStatus.setText(" "); // clear the status.
JOptionPane.showMessageDialog(this,
"Server still waits for a connection of Friend" +
" for previous game that has not connected yet!\n" +
"Try again later...",
"Server not ready!",
JOptionPane.ERROR_MESSAGE);
closeApplication(); // force to close.
else if (msg.equals("TERMINATED")) {        // server terminates our game!
lblStatus.setText(" "); // clear the status.
JOptionPane.showMessageDialog(this,
"Server terminated your game for no obvious reason!",
"Game terminated!",
JOptionPane.ERROR_MESSAGE);
closeApplication(); // force to close.
else if (msg.startsWith("CANCEL1:")) {   // 50:50 first canceled answer
try {
String index = extractData(msg);
cbAnswers[Integer.parseInt(index)-1].setText(" "); // clear.
} catch (Exception e) {
System.err.println("CANCEL1: -> " + e);
else if (msg.startsWith("CANCEL2:")) {   // 50:50 another canceled answer
try {
String index = extractData(msg);
cbAnswers[Integer.parseInt(index)-1].setText(" "); // clear.
} catch (Exception e) {
System.err.println("CANCEL2: -> " + e);
// clear the status & enable the buttons:
lblStatus.setText(" ");
enableButtons(true);
else if (msg.startsWith("BAR1:")) {  // help of the public (% for "A").
publicChart.setChart(extractData(msg), 1);
else if (msg.startsWith("BAR2:")) {  // help of the public (% for "B").
publicChart.setChart(extractData(msg), 2);
else if (msg.startsWith("BAR3:")) {  // help of the public (% for "C").
publicChart.setChart(extractData(msg), 3);
else if (msg.startsWith("BAR4:")) {  // help of the public (% for "D").
publicChart.setChart(extractData(msg), 4);
// assumed that "BAR4:?" is received as the last bar, so
// clear the status & enable the buttons:
lblStatus.setText(" ");
enableButtons(true);
public void sendToServer(String msg) {
if (thServer == null) // shuting down?
return;
out.println(msg);
// Flush the stream and check its error state:
if (out.checkError())
System.err.println("Cannot send -> " + msg);
else
System.out.println("SEND: " + msg);
* Asks user if he/she want's to restart the game.
* If the answer is "yes", starts new game.
private void askToRestart() {
int result;
result = JOptionPane.showConfirmDialog(this,
"Would you like to play again?",
"Play again?",
JOptionPane.YES_NO_OPTION,
JOptionPane.QUESTION_MESSAGE);
if (result == 0) {  // yes, restart.
lblStatus.setText("Waiting for server's response...");
sendToServer("RESTART"); // reset everything.
sendToServer("QUESTION"); // ask for a question.
else {              // no, close connection.
closeApplication(); // close connection, and exit.
* Closes this Game Client station.
private void closeApplication() {
// inform the server:
sendToServer("CLOSE");
thServer = null; // stop the thread.
try {
// close server streams:
out.close(); // close stream that sends data to server.
in.close(); // close stream that gets data from server.
// close socket connected to server:
if (socket != null)
socket.close();
} catch (IOException e) {}
// close everything:
System.exit(0);
* Enables (or disables) all buttons.
* @param b when true enables, otherwise disables.
private void enableButtons (boolean b) {
btnFinal.setEnabled(b);
btnFriend.setEnabled(b);
btn5050.setEnabled(b);
btnThePublic.setEnabled(b);
btnRetire.setEnabled(b);
* Prepares the GUI for the next question,
* hides the chart, resets question field, and possible
* answers.
private void prepareForNextQuestion() {
publicChart.setVisible(false);
lblQuestion.setText(" ");
for (int i=0; i<cbAnswers.length; i++) {
cbAnswers[i].setText("");
cbAnswers[i].setSelected(false); // reset selected check box.
selectedAnswer = -1;
private String indexToLetter(String index) {
String sANSWERS[] = {"\"A\"", "\"B\"", "\"C\"", "\"D\""};
try {
return sANSWERS[Integer.parseInt(index)-1];
} catch (Exception e) {
System.err.println("indexToLetter -> " + e);
return "?";
private static String extractData(String msg) {
try {
int i = msg.indexOf(':'); // get index of first ':'.
return msg.substring(i+1); // return second token.
catch(Exception e) {
return ""; // in case of error return empty string.
} // end of class.