Problem with a template method in JDialog

Question

Hi friends,
I'm experiencing a problem with JDialog. I have a base abstract class ChooseLocationDialog<E> to let a client choose a location for database. This is an abstract class with two abstract methods:
protected abstract E prepareLocation();
protected abstract JPanel prepareForm();Method prepareForm is used in the constructor of ChooseLocationDialog to get a JPanel and add it to content pane.
Method prepareLocation is used to prepare location of a database. I have to options - local file and networking.
There are two subclasses ChooseRemoteLocationDialog and ChooseLocalFileDialog.
When I start a local version, ChooseLocalFileDialog with one input field for local file, everything works fine and my local client version starts execution.
The problem arises when I start a network version of my client. Dialog appears and I can enter host and port into the input fields. But when I click Select, I get NullPointerException. During debugging I noticed that the values I entered into these fields ("localhost" for host and "10999" for port) were not set for corresponding JTextFields and when my code executes getText() method for these input fields it returns empty strings. This happens only for one of these dialogs - for the ChooseRemoteLocationDialog.
The code for ChooseLocationDialog class:
public abstract class ChooseLocationDialog<E> extends JDialog {
     private E databaseLocation;
     private static final long serialVersionUID = -1630416811077468527L;
     public ChooseLocationDialog() {
          setTitle("Choose database location");
          setAlwaysOnTop(true);
          setModal(true);
          Container container = getContentPane();
          JPanel mainPanel = new JPanel();
          //retrieving a form of a concrete implementation
          JPanel formPanel = prepareForm();
          mainPanel.add(formPanel, BorderLayout.CENTER);
          JPanel buttonPanel = new JPanel(new GridLayout(1, 2));
          JButton okButton = new JButton(new SelectLocationAction());
          JButton cancelButton = new JButton(new CancelSelectAction());
          buttonPanel.add(okButton);
          buttonPanel.add(cancelButton);
          mainPanel.add(buttonPanel, BorderLayout.SOUTH);
          container.add(mainPanel);
          pack();
          Toolkit toolkit = Toolkit.getDefaultToolkit();
          Dimension screenSize = toolkit.getScreenSize();
          int x = (screenSize.width - getWidth()) / 2;
          int y = (screenSize.height - getHeight()) / 2;
          setLocation(x, y);
          addWindowListener(new WindowAdapter() {
               @Override
               public void windowClosing(WindowEvent e) {
                    super.windowClosing(e);
                    System.exit(0);
     public E getDatabaseLocation() {
            return databaseLocation;
     protected abstract E prepareLocation();
     protected abstract JPanel prepareForm();
      * Action for selecting location.
      * @author spyboost
     private class SelectLocationAction extends AbstractAction {
          private static final long serialVersionUID = 6242940810223013690L;
          public SelectLocationAction() {
               putValue(Action.NAME, "Select");
          @Override
          public void actionPerformed(ActionEvent e) {
               databaseLocation = prepareLocation();
               setVisible(false);
     private class CancelSelectAction extends AbstractAction {
          private static final long serialVersionUID = -1025433106273231228L;
          public CancelSelectAction() {
               putValue(Action.NAME, "Cancel");
          @Override
          public void actionPerformed(ActionEvent e) {
               System.exit(0);
}Code for ChooseLocalFileDialog
public class ChooseLocalFileDialog extends ChooseLocationDialog<String> {
     private JTextField fileTextField;
     private static final long serialVersionUID = 2232230394481975840L;
     @Override
     protected JPanel prepareForm() {
          JPanel panel = new JPanel();
          panel.add(new JLabel("File"));
          fileTextField = new JTextField(15);
          panel.add(fileTextField);
          return panel;
     @Override
     protected String prepareLocation() {
          String location = fileTextField.getText();
          return location;
}Code for ChooseRemoteLocationDialog
public class ChooseRemoteLocationDialog extends
          ChooseLocationDialog<RemoteLocation> {
     private JTextField hostField;
     private JTextField portField;
     private static final long serialVersionUID = -2282249521568378092L;
     @Override
     protected JPanel prepareForm() {
          JPanel panel = new JPanel(new GridLayout(2, 2));
          panel.add(new JLabel("Host"));
          hostField = new JTextField(15);
          panel.add(hostField);
          panel.add(new JLabel("Port"));
          portField = new JTextField(15);
          panel.add(portField);
          return panel;
     @Override
     protected RemoteLocation prepareLocation() {
          String host = hostField.getText();
          int port = 0;
          try {
               String portText = portField.getText();
               port = Integer.getInteger(portText);
          } catch (NumberFormatException e) {
               e.printStackTrace();
          RemoteLocation location = new RemoteLocation(host, port);
          return location;
}Code for RemoteLocation:
public class RemoteLocation {
     private String host;
     private int port;
     public RemoteLocation() {
          super();
     public RemoteLocation(String host, int port) {
          super();
          this.host = host;
          this.port = port;
     public String getHost() {
          return host;
     public void setHost(String host) {
          this.host = host;
     public int getPort() {
          return port;
     public void setPort(int port) {
          this.port = port;
}Code snippet for dialog usage in local client implementation:
final ChooseLocationDialog<String> dialog = new ChooseLocalFileDialog();
dialog.setVisible(true);
location = dialog.getDatabaseLocation();
String filePath = location;Code snippet for dialog usage in network client implementation:
final ChooseLocationDialog<RemoteLocation> dialog = new ChooseRemoteLocationDialog();
dialog.setVisible(true);
RemoteLocation location = dialog.getDatabaseLocation();Exception that I'm getting:
Exception occurred during event dispatching:
java.lang.NullPointerException
     at suncertify.client.gui.dialog.ChooseRemoteLocationDialog.prepareLocation(ChooseRemoteLocationDialog.java:42)
     at suncertify.client.gui.dialog.ChooseRemoteLocationDialog.prepareLocation(ChooseRemoteLocationDialog.java:1)
     at suncertify.client.gui.dialog.ChooseLocationDialog$SelectLocationAction.actionPerformed(ChooseLocationDialog.java:87)
     at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
     at javax.swing.AbstractButton$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:6134)
     at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
     at java.awt.Component.processEvent(Component.java:5899)
     at java.awt.Container.processEvent(Container.java:2023)
     at java.awt.Component.dispatchEventImpl(Component.java:4501)
     at java.awt.Container.dispatchEventImpl(Container.java:2081)
     at java.awt.Component.dispatchEvent(Component.java:4331)
     at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4301)
     at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3965)
     at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3895)
     at java.awt.Container.dispatchEventImpl(Container.java:2067)
     at java.awt.Window.dispatchEventImpl(Window.java:2458)
     at java.awt.Component.dispatchEvent(Component.java:4331)
     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.pumpEventsForFilter(EventDispatchThread.java:178)
     at java.awt.Dialog$1.run(Dialog.java:1046)
     at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
     at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
     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)java version "1.6.0"
OpenJDK Runtime Environment (build 1.6.0-b09)
OpenJDK Client VM (build 1.6.0-b09, mixed mode, sharing)
OS: Ubuntu 8.04
Appreciate any help.
Thanks.
Edited by: spyboost on Jul 24, 2008 5:38 PM

Answer 1

What a silly error! I have to call Integer.parseInt instead of getInt. Integer.getInt tries to find a system property. A small misprint, but a huge amount of time to debug. I always use parseInt method and couldn't even notice that silly misprint. Sometimes it's useful to see the trees instead of whole forest :)
It works perfectly. Sorry for disturbing.