How to save component to jpg without jframe

Question

the code shows 2 methods to save component to jpg,
but if comment
f.getContentPane().add(lb);neither saveJPG_1() nor saveJPG_2() works.
can you explain why and how to work without jframe?
thanks.
public class Test1 {
      * @param args
      * @throws Exception
     public static void main(String[] args) throws Exception {
          new Test1().run();
     private void run() throws IOException {
          JLabel lb = new JLabel("Test Text");
          lb.setOpaque(true);
          JFrame f = new JFrame();          
          f.getContentPane().add(lb);
          f.pack();
          saveJPG_1(lb, new File("test1.jpg"));
          saveJPG_2(lb, new File("test2.jpg"));
          f.dispose();
     private void saveJPG_1(Component c, File file) throws IOException {
          Dimension dim = c.getPreferredSize();
          Image im = c.createImage(dim.width,dim.height);     
          c.paint(im.getGraphics());          
          ImageIO.write((RenderedImage)im, "jpg", file);
     private void saveJPG_2(Component c, File file) throws IOException {
          Dimension dim = c.getPreferredSize();
          BufferedImage im = new BufferedImage(dim.width,dim.height,BufferedImage.TYPE_INT_RGB);                    
          c.paint(im.getGraphics());
          ImageIO.write(im, "jpg", file);
}

Answer 1

Lazy loading is common place among variety of
systems.
Java GUI runtime must be doing it because on my
Linux/JDK 1.6(build 61), component c is null at:
c.paint(....);
when adding onto contentpane is commented out.Lazy loading means classes are loaded on demand and at the last moment possible. What makes you think that this allows for a variable to be null even after the component has been instantiated? And what does the Java "GUI runtime" have to do with it? It's the class loader that's responsible for this. It should be impossible for c to be null at that point in the code. You're using a beta JDK though right? Perhaps that's the culprit.
the code shows 2 methods to save component to jpg,
but if comment
f.getContentPane().add(lb);neither saveJPG_1() nor saveJPG_2() works.
can you explain why and how to work without jframe?
thanks.
public class Test1 {
      * @param args
      * @throws Exception
public static void main(String[] args) throws
s Exception {
          new Test1().run();
     private void run() throws IOException {
          JLabel lb = new JLabel("Test Text");
          lb.setOpaque(true);
          JFrame f = new JFrame();          
          f.getContentPane().add(lb);
          f.pack();
          saveJPG_1(lb, new File("test1.jpg"));
          saveJPG_2(lb, new File("test2.jpg"));
          f.dispose();
private void saveJPG_1(Component c, File file)
) throws IOException {
          Dimension dim = c.getPreferredSize();
          Image im = c.createImage(dim.width,dim.height);     
          c.paint(im.getGraphics());          
          ImageIO.write((RenderedImage)im, "jpg", file);
private void saveJPG_2(Component c, File file)
) throws IOException {
          Dimension dim = c.getPreferredSize();
BufferedImage im = new
ew
BufferedImage(dim.width,dim.height,BufferedImage.TYPE_
INT_RGB);                    
          c.paint(im.getGraphics());
          ImageIO.write(im, "jpg", file);
Can you display a JPanel on the screen without help? No. At some level it has to go back to a heavyweight widget. In this case the JFrame is that widget, so without it or a supplement you can't create the graphics context to create an Image of what that JPanel would look like displayed.