JFileChooser is throwing NullPointerException

Question

I have a swing application that is using JFileChooser. When I click the Open menu item from File menu it should show the File dialog box where user can select the file.

This application is running in my machine but encounters problem in another machine. File dialog box is not showing and stack trace shows that NullPointerException is thrown by JFileChooser

My machine is a 64 bit Windows 7 while the other machine is Windows 7 32 bit. Both machine are using java 1.6

To verify if its because of the 32-bit, I tried in another Windows 7 32-bit and the same application is working.

import javax.swing.JFileChooser;

import javax.swing.filechooser.FileNameExtensionFilter;

public class FileChooserTester{
   

    public Boolean loadMDBFile() {
      JFileChooser fc = new JFileChooser();
      FileNameExtensionFilter fileExtensionFilter = new FileNameExtensionFilter(
        "*.mdb", "mdb");
      fc.addChoosableFileFilter(fileExtensionFilter);
      fc.setDialogTitle("Open");

      int returnVal = fc.showOpenDialog(null);

      if (returnVal != JFileChooser.APPROVE_OPTION) {
       return null;
      } else {
       try {
       
        // process file

       } catch (Exception e) {
        e.printStackTrace();
        return false;
       }

       return true;
      }

     }
  
  
   public static void main(String[] args) {
           new FileChooserTester().loadMDBFile();
     
     }

Below is the stack trace.

ERROR actions.menu.File_Open - Error occured while opening an existing timetable. null 
caused by null java.lang.NullPointerException 
    at javax.swing.ImageIcon.<init><ImageIcon.java:215> 
    at javax.swing.ImageIcon.<init><ImageIcon.java:201>  
    at sun.swing.WindowPlaceBar.<init><WindowPlaceBar.java:94> 
    at com.sun.java.swing.plaf.windows.WindowFileChooserUI.updateUseShellFolder<WindowsFileChooserUI.java:542> 
    at com.sun.java.swing.plaf.windows.WindowFileChooserUI.installComponents<WindowsFileChooserUI.java:542> 
    at com.sun.java.swing.plaf.windows.WindowFileChooserUI.installComponents<WindowsFileChooserUI.java:219> 
    at java.swing.plaf.basic.basicFileChooserUI.installUI<BasicFileChooserUI.java:145> 
    at com.sun.java.swing.plaf.windows.WindowFileChooserUI.installUI<WindowsFileChooserUI.java:152> 
    at javax.swing.JComponent.setUI<JComponent.java:681> 
    at javax.swing.JFileChooser.updateUI<JFileChooser.java:1774> 
    at javax.swing.JFileChooser.setup<JFileChooser.java:371> 
    at javax.swing.JFileChooser.<init><JFileChooser.java:344> 
    at javax.swing.JFileChooser.<init><JFileChooser.java:297> 
    at actions.menu.File_Open.loadMDBFile<File_Open.java:221>

Thank you in advance.

Answer 1

Your problem is most likely caused by this part of the code:

if (returnVal != JFileChooser.APPROVE_OPTION) {
    return null;
}

This occurs when the cancel button or the 'X' is pressed. If you select a file and press the "open" button, the file should be processed normally.

My suggestion is to change the return type of the method to primitive boolean, and return false instead of null.

UPDATE: this is the converted version of your code I used to test (troubleshoot)

public static void main(String[] args)
{

    JFileChooser fc = new JFileChooser();
    FileNameExtensionFilter fileExtensionFilter = new FileNameExtensionFilter(
            "*.mdb", "mdb");
    fc.addChoosableFileFilter(fileExtensionFilter);
    fc.setDialogTitle("Open");

    int returnVal = fc.showOpenDialog(null);

    if (returnVal != JFileChooser.APPROVE_OPTION) {
        System.out.println("I am returning null!");
        System.exit(1);
    } else {
        try {

            System.out.println("Doing something");

        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("I am returning false");
            System.exit(-1);
        }

        System.out.println("I am returning true");
        System.exit(0);
    }
}