I want to draw a jpg image in a JFrame, so I used JPEGImageDecoder and read
it into a BufferedImage, which I draw to a JPanel.

But when I add the component (JPanel) to the JFrame, pack() doesn't work,
and I have to setSize() explicitly.

Why doesn't pack() work? I can't do imagePanel.getWidth() either, it's 0
until visible.
(Oh, I should mention, pack() still doesn't work after it's visible...do I
have to wait
until the image is rendered?)

Also, what's the best way to swap images dynamically in this case?

TIA
Jeff

////////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////
public class MyImagePanel {

  static String filename = "picture.jpg";

  public static void main(String[] args) {
      JFrame frame = new JFrame("MyImagePanel");
      frame.addWindowListener(new WindowAdapter() {
          public void windowClosing(WindowEvent e) {
              System.exit(0);
          }
      });

     MyImagePanel panel = new MyImagePanel();
     ImagePanel imagePanel = new ImagePanel(filename);

     frame.getContentPane().add(imagePanel, BorderLayout.CENTER);

frame.setSize((int)imagePanel.image.getWidth()+8,(int)imagePanel.image.getHe
ight()+22);
     frame.setLocation(100, 100);
     frame.setVisible(true);
  }
}

class ImagePanel extends JPanel {
  BufferedImage image;
  public ImagePanel(String filename) {
     try {
        InputStream in = getClass().getResourceAsStream(filename);
        JPEGImageDecoder decoder = JPEGCodec.createJPEGDecoder(in);
        image = decoder.decodeAsBufferedImage();
        in.close();
//         System.out.println((int)image.getWidth());
//         System.out.println((int)image.getHeight());
     } catch (Exception e) {
        System.out.println(e);
        System.exit(0);
     }
   }

   public void paintComponent(Graphics g) {
       g.drawImage(image, 0, 0, this);
   }
}