What's wrong with this code?

Question

I wrote this code:

public class FileViewer extends JPanel implements ActionListener {

/**
 * 
 */
private static final long serialVersionUID = 1L;

JFileChooser chooser;

FileNameExtensionFilter filter = null;

JEditorPane pane = null;

JTextField text = null;

JButton button;

JTextArea o = null;

URL url;

public FileViewer(JTextArea o) {
 this.o = o;
 setLayout(new FlowLayout(FlowLayout.RIGHT));
 JTextField text = new JTextField("file...", 31);
 text.setColumns(45);
 text.revalidate();
 text.setEditable(true);

 button = new JButton("Browse");
 add(text);
 add(button);
 filter = new FileNameExtensionFilter("html", "html");
 chooser = new JFileChooser();
 chooser.addChoosableFileFilter(filter);

 button.addActionListener(this);

}

public void paintComponent(Graphics g) {
 super.paintComponents(g);
 Graphics2D graphic = (Graphics2D) g;
 graphic.drawString("HTML File:", 10, 20);

}

public void actionPerformed(ActionEvent event) {
 int returnVal = 0;
 if (event.getSource() == button) {
  returnVal = chooser.showOpenDialog(FileViewer.this);
  if (returnVal == JFileChooser.APPROVE_OPTION) {
   text.setToolTipText(chooser.getSelectedFile().getName());

  } else
   o.append("Open command cancled by user.");
   }
     }
}

But in the line: text.setToolTipText(chooser.getSelectedFile().getName()); a NullPointerException is thrown!

EDIT I have fixed the problem which I have mentioned above but it doesn't work correctly (it doesn't write the name of the file in the text!) :-(

Answer 1

You've declared text globally and assigned NULL to it. In your constructor for FileViewer you declare it again with new, but this declaration is local. The variable referenced in actionPerformed() is the global one, which is still NULL, so you get the exception. If you change

JTextField text = new JTextField("file...", 31);

to

text = new JTextField("file...", 31);

that should fix it.

Answer 2

replace this:

JTextField text = new JTextField("file...", 31);

with this:

text = new JTextField("file...", 31);

Answer 3

The field text is null as in your FileViewer constructor you have created a local variable called text that has been added to the form.

Replace

JTextField text = new JTextField("file...", 31);

with

text = new JTextField("file...", 31);

Answer 4

Answering your other point:

text.setToolTipText(chooser.getSelectedFile().getName());

Was this the intended behaviour? The filename will only appear as a tooltip when you mouse over the text field. To put text directly into a JTextField you should call setText() instead.

Answer 5

setToolTipText method does not set the text. It sets the tooltip text, which is shown when mouse hovers the text. Use setText method.