How to update an image inside a JLabel and post that to the screen

Question

I am attempting to write a program that will loop through lots of images and apply various operations to them and then store use the result to train a self organizing map, i wish to write a front end to this program that for each image i am processing it will display the original and it will display the resultant image after i have applied the operations to it, so far i have written a GUI and from what i have researched it should display the image ( which i have scaled because some can be rather large ) on the left of the screen but nothing is displayed apart from the text labels i was hoping for some incite into what is going wrong as i am new to programming GUI's.

This is what i get when i run the program, what i would like is a image displayed below the "Origonal Image" label

This portion of code just handles the initialization as you can see an panel is added to the frame all the program is inside here. When the panel is initialized the following code is run, note that this is inside the ImageComparatorPanel class

public ImageComparatorPanel() throws FileNotFoundException, UnsupportedEncodingException
{
    setLayout(new BorderLayout());

    origonalImage = new JLabel( new ImageIcon() );
    leftTitle = new JLabel("Origonal Image");
    rightTitle = new JLabel("Shrunken Image");

    ButtonListener listener = new ButtonListener();

    start = new JButton("Start!");
    start.addActionListener(listener);

    JPanel left = new JPanel();
    left.add(leftTitle);
    left.add(origonalImage);

    //add(leftTitle, BorderLayout.WEST);
    //add(origonalImage, BorderLayout.WEST);
    add(left, BorderLayout.WEST);
    add(rightTitle, BorderLayout.EAST);
    add(start, BorderLayout.NORTH);

    setPreferredSize(new Dimension(800,800));

}

in the main part of my program ( the bit that is executed when the start button is pressed ) the bit of code that is supposed to update the image is as follows

origonalImage.setIcon(getImage(imagePath));

the getImage function opens the image and shrinks it so that it will fit on the panel the code for this is ( thought i should include this just in case...

public ImageIcon getImage(String URL) throws IOException
{
    double scale = 0.5;

    File f = new File(URL);
    Image image = ImageIO.read(f);

    ImageIcon icon = new ImageIcon(image);
    int h = icon.getIconHeight();
    int w = icon.getIconWidth();

    Image newImg = icon.getImage();
    Image scaled = newImg.getScaledInstance((int)(w * scale), (int)(h * scale), Image.SCALE_SMOOTH);

    ImageIcon newIcon = new ImageIcon(scaled);

    return newIcon;
}

How can i change this so on each iteration of the loop in the RUN function the image displayed in the GUI will be updated?

Answer 1

You state:

How can i change this so on each iteration of the loop in the RUN function the image displayed in the GUI will be updated?

To change a GUI's visible state every x msecs, you need to either use a Swing Timer or a background thread such as a SwingWorker.

The Timer would be used if your code being called intermittently is not long running and does not tie up the Swing event thread (the Event Dispatch Thread or EDT) inordinately. If the code being called periodically does take time to run, then this technique will tie up the EDT making your GUI completely unresponsive. In this case, use the SwingWorker when you do in fact need to do heavy processing between image changes, and then use the SwingWorker's publish/process method pair to obtain and display updated images. A properly created SwingWorker will run the heavy lifting code in a thread background to the EDT, but will allow you to make Swing calls on the EDT when necessary.

If your main problem is just that no images are showing, then you're going about solving this wrong: you shouldn't be trying to solve this in a huge complex program but instead create a small program that just tries to show an image and nothing else. Solve each small sub-problem in a step-wise fashion, and only when solved, add it to the greater whole, the large program.