Question

I’m having a bit of a problem with a program I’m trying to write. I want to be able to get pictures from a filechooser and print them on a JPanel. Now the retrieving of the pictures works but I can’t seem to be able to put them in an array of JLabels, I get a NullPointerException. I know what this exception means but I don’t see where or how I did something wrong, Could someone help me find my mistake?

private class OpenFileHandler implements ActionListener {

    public BufferedImage [] getBufferedImages() {
        chooser = new JFileChooser();
        chooser.setMultiSelectionEnabled(true);
        chooser.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);
        chooser.setFileFilter(new FileNameExtensionFilter("Images", "PNG", "JPG", "GIF", "BMP"));
        int result = chooser.showOpenDialog(null);

        if (result == JFileChooser.APPROVE_OPTION) {
            imagesFile = chooser.getSelectedFiles();
        }

        imagesBuf = new BufferedImage[imagesFile.length];

        for (int i = 0; i<imagesFile.length; i++) {
            try {
                imagesBuf[i] = ImageIO.read(imagesFile[i]);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return imagesBuf;
    }

    public void actionPerformed(ActionEvent event) {
        if (event.getSource() == openMenu) {
            getBufferedImages();

            for (int i = 0; i<imagesBuf.length; i++) {
                labels[i] = new JLabel(new ImageIcon(imagesBuf[i]));
                picturePanel.add(labels[i]);
            }
        }
    }
}

And this is the error I’m getting:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at be.maarten.gallery.GalleryFrame$OpenFileHandler.actionPerformed(GalleryFrame.java:118)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.AbstractButton.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

If your GalleryFrame line 118 is pointing to line below:

 picturePanel.add(labels[i]);

Then I think that picturePanel is not initialized. Please correct/perform the initialization before its usage in actionPerformed method. It should work fine.

If this is not the case, please share the statement at line 118.