Thread: NullPointerException on ActionListeners

Hey guys, new to the forum, hope you're all well and looking forward to Christmas! Okay, so I'm trying to write a simple web browser, only every time I press a button or hit enter in the url field etc, anything which uses an ActionListener, nothing happens and I get stuff such as this in my debug output window :

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at WebBrowser.backButtonActionPerformed(WebBrowser.java:113)
    at WebBrowser.access$000(WebBrowser.java:9)
    at WebBrowser$1.actionPerformed(WebBrowser.java:39)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
    at java.awt.Component.processMouseEvent(Component.java:6263)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3255)
    at java.awt.Component.processEvent(Component.java:6028)
    at java.awt.Container.processEvent(Container.java:2041)
    at java.awt.Component.dispatchEventImpl(Component.java:4630)
    at java.awt.Container.dispatchEventImpl(Container.java:2099)
    at java.awt.Component.dispatchEvent(Component.java:4460)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4574)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
    at java.awt.Container.dispatchEventImpl(Container.java:2085)
    at java.awt.Window.dispatchEventImpl(Window.java:2475)
    at java.awt.Component.dispatchEvent(Component.java:4460)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

My menus work just fine which is odd as they use ActionListeners

Okay, my full code...this is gonna be big:

import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;
import java.io.IOException;
 
public class WebBrowser extends JFrame implements HyperlinkListener{
 
	private JButton backButton, forwardButton;
	private JTextField urlField;
	private JEditorPane htmlPane;
	private ArrayList pageList = new ArrayList();
	private String defaultTitle = ("G52GUI Web Browser");
 
	public WebBrowser(String initURL) {
 
		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		this.setTitle("HTML Viewer Example");
		setSize(800, 600);
 
		JPanel navBarPanel = new JPanel();
        JButton backButton = new JButton("Back");
        JButton forwardButton = new JButton("Forward");
        JTextField urlField = new JTextField(35);
        JButton goButton = new JButton("Go");
        JEditorPane htmlPane = new JEditorPane();
        JMenuBar menuBar = new JMenuBar();
        JMenu fileMenu = new JMenu("File");
        JMenuItem exitMenuItem = new JMenuItem("Exit");
        JMenu bookmarksMenu = new JMenu("Bookmarks");
        JMenuItem bookmarkMenuItem = new JMenuItem("Bookmark This Page");
 
        navBarPanel.setBorder(BorderFactory.createEtchedBorder());
 
        backButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                backButtonActionPerformed();
            }
        });
 
		navBarPanel.add(backButton);
 
        forwardButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                forwardButtonActionPerformed();
            }
        });
 
        navBarPanel.add(forwardButton);
 
        urlField.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                urlFieldActionPerformed();
            }
        });
 
        navBarPanel.add(urlField);
 
        htmlPane.setContentType("text/html");
        htmlPane.setEditable(false);
		htmlPane.addHyperlinkListener(this);
 
        goButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                goButtonActionPerformed();
            }
        });
 
        navBarPanel.add(goButton);
 
        exitMenuItem.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_Q, InputEvent.CTRL_MASK));
        exitMenuItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                exitMenuItemActionPerformed();
            }
        });
 
        fileMenu.add(exitMenuItem);
 
        menuBar.add(fileMenu);
 
        bookmarkMenuItem.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_D, InputEvent.CTRL_MASK));
        bookmarksMenu.add(bookmarkMenuItem);
 
        menuBar.add(bookmarksMenu);
 
        setJMenuBar(menuBar);
 
        getContentPane().setLayout(new BorderLayout());
        getContentPane().add(navBarPanel, BorderLayout.NORTH);
        getContentPane().add(new JScrollPane(htmlPane),
                BorderLayout.CENTER);
 
		verifyAndLoad(initURL);
 
	}
 
    private void exitMenuItemActionPerformed() {                                             
        System.exit(0);
    }                                            
 
    private void urlFieldActionPerformed() {                                         
        verifyAndLoad(urlField.getText());
    }                                        
 
    private void goButtonActionPerformed() {                                         
        verifyAndLoad(urlField.getText());
    }                                        
 
    private void backButtonActionPerformed() {                                           
        URL currentURL = htmlPane.getPage();
        int pageIndex = pageList.indexOf(currentURL.toString());
        try {
            loadURL(new URL((String) pageList.get(pageIndex - 1)), false);
        } catch (Exception e) {}
    }                                          
 
    private void forwardButtonActionPerformed() {                                              
        URL currentURL = htmlPane.getPage();
        int pageIndex = pageList.indexOf(currentURL.toString());
        try {
            loadURL(new URL((String) pageList.get(pageIndex + 1)), false);
        } catch (Exception e) {}
    }                                             
 
    public void hyperlinkUpdate(HyperlinkEvent evt) {                                         
        if (evt.getEventType() == HyperlinkEvent.EventType.ACTIVATED)
        {
           try {
             htmlPane.setPage(evt.getURL());
             urlField.setText(evt.getURL().toExternalForm());
           } catch(IOException ioe) {
             errorMessage("Can't follow link to "
                      + evt.getURL().toString());
           }
         }
    }   
 
    private void verifyAndLoad(String url) {
        URL verifiedURL = verifyUrl(url);
        if(verifiedURL != null)
        {
            loadURL(verifiedURL, true);
        } else {
            errorMessage("Invalid URL");
        }
    }
 
    private URL verifyUrl(String url) {
        if (!url.toLowerCase().startsWith("http://www."))
        {
            url = "http://www."+url;
            urlField.setText(url);
        }
        URL verifiedUrl = null;
        try {
            verifiedUrl = new URL(url);
        } catch (MalformedURLException ex) {
            return null;
        }
        return verifiedUrl;
    }
 
    private void loadURL(URL pageAddress, boolean addToList) {
        setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));
        setTitle("Loading...");
        try {
            URL currentURL = htmlPane.getPage();
            htmlPane.setPage(pageAddress);
            if (addToList) {
                int listSize = pageList.size();
                if (listSize > 0) {
                    int pageIndex = pageList.indexOf(currentURL.toString());
                    if (pageIndex < listSize - 1) {
                        for (int i = listSize - 1; i > pageIndex; i--) {
                            pageList.remove(i);
                        }
                    }
                }
             }
             pageList.add(pageAddress.toString());
             urlField.setText(pageAddress.toString());
        } catch (Exception ex) {
                errorMessage("Cannot load " + pageAddress.toString());
        }
         setCursor(Cursor.getDefaultCursor());
         setTitle(defaultTitle);
    }
 
    private void errorMessage(String error) {
    JOptionPane.showMessageDialog(this, error, "Error",
                                  JOptionPane.ERROR_MESSAGE);
 
    }
 
     public static void main(String[] args) {
        WebBrowser frame = new WebBrowser("http://www.google.co.uk");
        frame.setVisible(true);
    }
 
}

If you help I will give you a cookie! Only, not a real one cos I don't know where you live. But the thought is there!

EDIT:

NEVERMIND! I was stupid, I made my buttons and urlField, and then created local versions in my constructor. My other methods were using the global variables which of course hadn't been initialised.