Hi all gurus:
in the following program for displaying image I try to
get the width/height of the image. The first attempt
(marked with first) before setVisible() returns -1/-1,
only the second attempt returns the correct values. But
if I remove the first one, the second one returns ALSO
-1/-1. I don't understand this behavior. I thought that
after the variable "image" is instantiated (in the
constructor, the width/height data must already be
available.
What measure must be taken in order to get the correct
data before the frame becomes visible? Thanks in advance

k.wang

// the program:
import java.awt.*;
import javax.swing.*;
public class ImgDisplayer extends JPanel {
 String imageFile = "images/rocketship.gif";
 Image image;
 public ImgDisplayer() {
   super();
   image = Toolkit.getDefaultToolkit().getImage(imageFile);
 }
 public void paintComponent(Graphics g) {
   super.paintComponent(g);
   g.drawImage(image, 0, 0, this);
 }
 private int getImageWidth() {
   return image.getWidth(this);
 }
 private int getImageHeight() {
   return image.getHeight(this);
 }
 public static void main(String[] args) {
   int width, height;
   JFrame frame = new JFrame("Image Displayer");
   ImgDisplayer imgDisp = new ImgDisplayer();
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   frame.getContentPane().add(imgDisp);
   frame.setSize(120, 120);
   width = imgDisp.getImageWidth();               // First
   height = imgDisp.getImageHeight();
System.out.println("First " + width + " " + height);
   frame.setVisible(true);
   width = imgDisp.getImageWidth();               // Second
   height = imgDisp.getImageHeight();
System.out.println("Second " + width + " " + height);
 }
}