File exists warning

Question

I wanted to write a generic solution for save dialogs where you're going to be overwriting the file. Because getSelectedFile is called a whole bunch before the dialog is closed and a choice made, the only way I could figure out how to do it was to add a PropertyChangeListener and listen for the ancestor property.
Is there a better way to do this?
here's my code
* Created on May 17, 2005 by @author Tom Jacobs
package tjacobs.ui;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.io.File;
import javax.swing.JOptionPane;
import javax.swing.filechooser.FileFilter;
import javax.swing.filechooser.FileSystemView;
import tjacobs.ui.fc.FileExtensionFilter;
public class JFileChooser extends javax.swing.JFileChooser {
     private boolean mWarnOnWriteOver = false;
     private boolean mAncestorNull = false;
     public JFileChooser() {
          super();
          init();
     private void init() {
          addPropertyChangeListener(new PropertyChangeListener() {
               public void propertyChange(PropertyChangeEvent pe) {
                    //System.out.println("Here");
                    System.out.println(pe.getPropertyName() + ": " + pe.getNewValue());
                    if (pe.getPropertyName().equals("ancestor") && pe.getNewValue() == null) {
                         mAncestorNull = true;
     public JFileChooser(String arg0) {
          super(arg0);
          init();
     public JFileChooser(File arg0) {
          super(arg0);
          init();
     public JFileChooser(FileSystemView arg0) {
          super(arg0);
          init();
     public JFileChooser(File arg0, FileSystemView arg1) {
          super(arg0, arg1);
          init();
     public JFileChooser(String arg0, FileSystemView arg1) {
          super(arg0, arg1);
          init();
     public boolean getWarnOnWriteOver() {
          return mWarnOnWriteOver;
     public void setWarnOnWriteOver(boolean b) {
          mWarnOnWriteOver = b;
     public File getSelectedFile() {
          File f = super.getSelectedFile();
          if (f == null) return f;
          if (getDialogType() == super.SAVE_DIALOG && f.getName().indexOf(".") == -1) {
               //check if it's using file extension filter. If so, add the filter extension
               FileFilter ff = getFileFilter();
               if (ff instanceof FileExtensionFilter) {
                    String ending = ((FileExtensionFilter)ff).getType();
                    f = new File(f.getParent() + getName() + ending);
               //now check if it's overwriting another file
          //System.out.println("isVisible: " + this.isVisible());
          if (mWarnOnWriteOver && mAncestorNull) {
               if (f.exists()) {
                    int ans = JOptionPane.showConfirmDialog(null, "" + f.getName() + " exists. Overwrite?", "Save Over Existing File", JOptionPane.OK_CANCEL_OPTION, JOptionPane.QUESTION_MESSAGE);
                    if (ans == JOptionPane.OK_OPTION)
                         return f;
                    return null;
          return f;
}

Answer 1

I would go the composition route rather than the inheritance route in this case. Then you won't have to worry about all the internal workings of a JFileChooser:
public interface FileSelector {
    public File getFileToSave(..., boolean warnIfExists);
    public File getFileToOpen(...);
class FileSelectorImpl implements FileSelector {
    private JFileChooser fc;
    public File getFileToSave(..., boolean warnIfExists) {
        // Get the File the standard way from the internal JFileChooser.
        // If it exists and warnIfExists is true, show the confirmation dialog
}