Null Pointer exception returned when object is not null!

Question

I've isolated the problem and cut down the code to the minimum. Why do I get a null pointer exception when the start method is called, when the object objJTextField is not null at this point???? I'm really stuck here, HELP!
(two small java files, save as BasePage.java and ExtendedPage.java and then run ExtendedPage)
first file
~~~~~~~
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public abstract class BasePage extends JFrame implements ActionListener
private JPanel objJPanel = null;
public BasePage()
setSize(300,200);
Container objContentPane = getContentPane();
objJPanel = new JPanel();
createObjects();
createPage();
// Add panels to content pane
objContentPane.add(objJPanel);
public void addComponentToPage(JComponent objJComponent)
objJPanel.add(objJComponent);
public void addButtonToPage(JButton objJButton)
objJButton.addActionListener(this);
objJPanel.add(objJButton);
public void actionPerformed(ActionEvent objActionEvent)
System.out.println("Action performed");
userDefinedButtonClicked(objActionEvent.getActionCommand());
// overide
public abstract void createObjects();
public abstract void createPage();
public abstract void userDefinedButtonClicked(String sActionCommand);
file 2
~~~~
import javax.swing.*;
public class ExtendedPage extends BasePage
private JTextField objJTextField = null;
private JButton objJButtonBrowse = null;
public ExtendedPage()
super();
public void createObjects()
objJTextField = new JTextField(20);
objJButtonBrowse = new JButton("Start");
objJButtonBrowse.setActionCommand("START");
public void createPage()
addComponentToPage(objJTextField);
addButtonToPage(objJButtonBrowse);
public void userDefinedButtonClicked(String sActionCommand)
if ((sActionCommand != null) && (sActionCommand.equals("START")) )
start();
private void start()
objJTextField.setText("Doesn't work");
public static void main(String[] args)
ExtendedPage objEP = new ExtendedPage();
objEP.show();

Answer 1

Hello ppaulf,
Your problem is in your ExtendedPage.java file. You can fix this by changing the line
private JTextField objJTextField = null;to:
private JTextField objJTextField = new JTextField();This creates a proper instance.
Good luck,
Ming
Developer Technical Support
http://www.sun.com/developers/support