Urgent: Getting the 'Cancel' button to work

Question

Hi everyone!!!
I am having problems with a button that should close a JFrame that is created in another class file. Basically I dont know how to pass the required object (that is the "NewWizardFrame" object) through to the action listener for the cancel button that exists as a inner class within "NewWizardPanel". I am getting nullpointerexceptions when I click on the 'cancel' button to close the frame. I will post all the code below so that anyone can compile it and see what the hell i'm going on about!!! If you know how to fix the problem just post the fixed code back here and everything will be perfect!!! Thanks
p.s. I will give 5 duke dollars to the first person who can post me back the fixed code. Thanks again.
The code follows below, just run the NewChartTest file.
* NewChartTest.java
* 23/11/02 (Date start)
* This class is for test purposes for
* the "New Chart" wizard
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
public class NewChartTest extends JPanel
private JButton newButton;
public JFrame wizardFrame;
public NewChartTest()
// create new button
newButton = new JButton("New Chart");
// create tooltip for every button
newButton.setToolTipText("New Chart");
// add our button to the JPanel
add(newButton);
// construct button action
NewButtonListener listener1 = new NewButtonListener();
// Add action listener to button
newButton.addActionListener(listener1);
private class NewButtonListener implements ActionListener
public void actionPerformed(ActionEvent evt)
wizardFrame = new JFrame("New Chart Wizard*");
NewWizardPanel wizardPanel = new NewWizardPanel();
wizardFrame.getContentPane().add(wizardPanel);
wizardFrame.setSize(380, 220);
wizardFrame.setVisible(true);
// Main entry point into the ToolBarPanel class
public static void main(String[] args)
// Create a frame to hold us and set its title
JFrame frame = new JFrame("New Chart Test");
// Set frame to close after user request
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Add our tab panel to the frame
NewChartTest nct = new NewChartTest();
frame.getContentPane().add(nct, BorderLayout.CENTER);
// Resize the frame
frame.setSize(680, 480);
// Make the windows visible
frame.setVisible(true);
* NewWizardPanel.java
* 23/11/02 (Date start)
* This class is for test purposes for
* the "New Chart" wizard
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
public class NewWizardPanel extends JPanel
private JLabel projectNameLabel;
private JLabel maxCharacterLabel;
private JLabel durationLabel;
private JLabel monthLabel;
private JTextField projectName;
private JComboBox projectDuration;
private JButton okButton;
private JButton cancelButton;
private JFrame wizardFrame;
public NewWizardPanel()
// create additional panels to hold objects
JPanel topPanel = new JPanel();
JPanel lowerPanel = new JPanel();
JPanel buttonPanel = new JPanel();
// Create a border around the "nextpanel"
Border etched = BorderFactory.createBevelBorder(BevelBorder.RAISED, Color.black, Color.blue);
Border titled = BorderFactory.createTitledBorder(etched, "Please provide a title to your project");
topPanel.setBorder(titled);
// Create a border around the "lowerpanel"
Border etched1 = BorderFactory.createBevelBorder(BevelBorder.RAISED, Color.black, Color.blue);
Border titled1 = BorderFactory.createTitledBorder(etched1, "Please select the duration of your project");
lowerPanel.setBorder(titled1);
// initialise label objects
projectNameLabel = new JLabel("Project Name", JLabel.LEFT);
maxCharacterLabel = new JLabel("(Max 20 Chars)");
durationLabel = new JLabel("Duration (in months)", JLabel.LEFT);
monthLabel = new JLabel("1 - 12 months");
projectName = new JTextField("Default Name", 20);
projectName.setColumns(15);
topPanel.validate();
projectDuration = new JComboBox();
projectDuration.setEditable(false);
projectDuration.addItem("1");
projectDuration.addItem("2");
projectDuration.addItem("3");
projectDuration.addItem("4");
projectDuration.addItem("5");
projectDuration.addItem("6");
projectDuration.addItem("7");
projectDuration.addItem("8");
projectDuration.addItem("9");
projectDuration.addItem("10");
projectDuration.addItem("11");
projectDuration.addItem("12");
// initialise buttons
okButton = new JButton("Ok", new ImageIcon("Test/ok.gif"));
cancelButton = new JButton("Cancel", new ImageIcon("Test/cancel.gif"));
// add objects to panels
topPanel.add(projectNameLabel);
topPanel.add(projectName);
topPanel.add(maxCharacterLabel);
lowerPanel.add(durationLabel);
lowerPanel.add(projectDuration);
lowerPanel.add(monthLabel);
buttonPanel.add(okButton);
buttonPanel.add(cancelButton);
// create instance of cancelButtonListener
CancelButtonListener cancelListen = new CancelButtonListener(wizardFrame);
// add actionListener for the cancel button
cancelButton.addActionListener(cancelListen);
// use Box layout to arrange panels
Box hbox2 = Box.createHorizontalBox();
hbox2.add(topPanel);
Box hbox4 = Box.createHorizontalBox();
hbox4.add(lowerPanel);
Box hbox5 = Box.createHorizontalBox();
hbox5.add(buttonPanel);
Box vbox = Box.createVerticalBox();
vbox.add(hbox2);
vbox.add(Box.createGlue());
vbox.add(hbox4);
vbox.add(Box.createGlue());
vbox.add(hbox5);
this.add(vbox, BorderLayout.NORTH);
private class CancelButtonListener implements ActionListener
public CancelButtonListener(JFrame awizardFrame)
wizardFrame = awizardFrame;
public void actionPerformed(ActionEvent event)
Object source = event.getSource();
if(source == cancelButton)
wizardFrame.setVisible(false);
// Main entry point into the ToolBarPanel class
public static void main(String[] args)
// Create a frame to hold us and set its title
JFrame frame = new JFrame("New Chart Wizard");
// Set frame to close after user request
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Add our tab panel to the frame
NewWizardPanel nwp = new NewWizardPanel();
frame.getContentPane().add(nwp, BorderLayout.CENTER);
// Resize the frame
frame.setSize(680, 480);
// Make the windows visible
frame.setVisible(true);

Answer 1

Hi everyone!!!
I am having problems with a button that should close a
JFrame that is created in another class file.
Basically I dont know how to pass the required object
(that is the "NewWizardFrame" object) through to the
action listener for the cancel button that exists as a
inner class within "NewWizardPanel". I am getting
nullpointerexceptions when I click on the 'cancel'
button to close the frame. I will post all the code
below so that anyone can compile it and see what the
hell i'm going on about!!! If you know how to fix the
problem just post the fixed code back here and
everything will be perfect!!! Thanks
p.s. I will give 5 duke dollars to the first person
who can post me back the fixed code. Thanks again.
The code follows below, just run the NewChartTest
file.
* NewChartTest.java
* 23/11/02 (Date start)
* This class is for test purposes for
* the "New Chart" wizard
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
public class NewChartTest extends JPanel
private JButton newButton;
public JFrame wizardFrame;
static NewChartTest instance;
public NewChartTest()
{  instance = this;
>
// create new button
newButton = new JButton("New Chart");
// create tooltip for every button
newButton.setToolTipText("New Chart");
// add our button to the JPanel
add(newButton);
// construct button action
NewButtonListener listener1 = new
1 = new NewButtonListener();
// Add action listener to button
newButton.addActionListener(listener1);
private class NewButtonListener implements
nts ActionListener
public void actionPerformed(ActionEvent evt)
wizardFrame = new JFrame("New Chart
("New Chart Wizard*");
NewWizardPanel wizardPanel = new
Panel = new NewWizardPanel();
wizardFrame.getContentPane().add(wizardPanel);
wizardFrame.setSize(380, 220);
wizardFrame.setVisible(true);
// Main entry point into the ToolBarPanel class
public static void main(String[] args)
// Create a frame to hold us and set its
set its title
JFrame frame = new JFrame("New Chart Test");
// Set frame to close after user request
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Add our tab panel to the frame
NewChartTest nct = new NewChartTest();
frame.getContentPane().add(nct,
dd(nct, BorderLayout.CENTER);
// Resize the frame
frame.setSize(680, 480);
// Make the windows visible
frame.setVisible(true);
* NewWizardPanel.java
* 23/11/02 (Date start)
* This class is for test purposes for
* the "New Chart" wizard
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
public class NewWizardPanel extends JPanel
private JLabel projectNameLabel;
private JLabel maxCharacterLabel;
private JLabel durationLabel;
private JLabel monthLabel;
private JTextField projectName;
private JComboBox projectDuration;
private JButton okButton;
private JButton cancelButton;
private JFrame wizardFrame;
public NewWizardPanel()
// create additional panels to hold objects
JPanel topPanel = new JPanel();
JPanel lowerPanel = new JPanel();
JPanel buttonPanel = new JPanel();
// Create a border around the "nextpanel"
Border etched =
tched =
BorderFactory.createBevelBorder(BevelBorder.RAISED,
Color.black, Color.blue);
Border titled =
itled = BorderFactory.createTitledBorder(etched,
"Please provide a title to your project");
topPanel.setBorder(titled);
// Create a border around the "lowerpanel"
Border etched1 =
ched1 =
BorderFactory.createBevelBorder(BevelBorder.RAISED,
Color.black, Color.blue);
Border titled1 =
tled1 = BorderFactory.createTitledBorder(etched1,
"Please select the duration of your project");
lowerPanel.setBorder(titled1);
// initialise label objects
projectNameLabel = new JLabel("Project Name",
Name", JLabel.LEFT);
maxCharacterLabel = new JLabel("(Max 20
(Max 20 Chars)");
durationLabel = new JLabel("Duration (in
ion (in months)", JLabel.LEFT);
monthLabel = new JLabel("1 - 12 months");
projectName = new JTextField("Default Name",
Name", 20);
projectName.setColumns(15);
topPanel.validate();
projectDuration = new JComboBox();
projectDuration.setEditable(false);
projectDuration.addItem("1");
projectDuration.addItem("2");
projectDuration.addItem("3");
projectDuration.addItem("4");
projectDuration.addItem("5");
projectDuration.addItem("6");
projectDuration.addItem("7");
projectDuration.addItem("8");
projectDuration.addItem("9");
projectDuration.addItem("10");
projectDuration.addItem("11");
projectDuration.addItem("12");
// initialise buttons
okButton = new JButton("Ok", new
k", new ImageIcon("Test/ok.gif"));
cancelButton = new JButton("Cancel", new
l", new ImageIcon("Test/cancel.gif"));
// add objects to panels
topPanel.add(projectNameLabel);
topPanel.add(projectName);
topPanel.add(maxCharacterLabel);
lowerPanel.add(durationLabel);
lowerPanel.add(projectDuration);
lowerPanel.add(monthLabel);
buttonPanel.add(okButton);
buttonPanel.add(cancelButton);
// create instance of cancelButtonListener
CancelButtonListener cancelListen = new
n = new CancelButtonListener(wizardFrame);
// add actionListener for the cancel button
cancelButton.addActionListener(cancelListen);
// use Box layout to arrange panels
Box hbox2 = Box.createHorizontalBox();
hbox2.add(topPanel);
Box hbox4 = Box.createHorizontalBox();
hbox4.add(lowerPanel);
Box hbox5 = Box.createHorizontalBox();
hbox5.add(buttonPanel);
Box vbox = Box.createVerticalBox();
vbox.add(hbox2);
vbox.add(Box.createGlue());
vbox.add(hbox4);
vbox.add(Box.createGlue());
vbox.add(hbox5);
this.add(vbox, BorderLayout.NORTH);
private class CancelButtonListener implements
nts ActionListener
public CancelButtonListener(JFrame
(JFrame awizardFrame)
public void actionPerformed(ActionEvent
onEvent event)
Object source = event.getSource();
if(source == cancelButton)
NewChartTest.instance.wizardFrame.setVisible(false);
// Main entry point into the ToolBarPanel class
public static void main(String[] args)
// Create a frame to hold us and set its
set its title
JFrame frame = new JFrame("New Chart
w Chart Wizard");
// Set frame to close after user request
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Add our tab panel to the frame
NewWizardPanel nwp = new NewWizardPanel();
frame.getContentPane().add(nwp,
dd(nwp, BorderLayout.CENTER);
// Resize the frame
frame.setSize(680, 480);
// Make the windows visible
frame.setVisible(true);