Problem with creating and displaying images in a thread

Question

Hi everyone,
i need some bit of advice (of course otherwise i wouldn't write anything here). My situation is like this:
I have a JFrame where the user can enter a string. Then a file that corresponds to this string is read and the information is stored in objects, then these two objects (there are always 2 objects per file) are passed to an ImageCreator class that creates one image with the information found in each object. So per file there are always two images created. Now the thing is that after creating the images i need to display them for 10 seconds each, but as it takes about 2 seconds to create each image i would like to start showing the first one already while the second one is still being created. As i am not really experienced with threads i wonder what would be the best way to manage something like this. Here is a little bit of code, which is still in a rather pseudo code state...if(checkPattern(scanField.getText()) &&
      fc.getFile(createFilename(scanField.getText())) != null)
      BufferedImage img = null;
      ImageDisplay display = new ImageDisplay(scanField.getText(), this);
      for (int i=1; i<3; i++) {
      Info info = tReader.readTelegramForOneInfo(createFilename(scanField.getText()));
      if(i==1) 
        info.setError(ew.getProperty(info.getMTNr1(), info.getLack()));
      if(i==2)
        info.setError(ew.getProperty(info.getMTNr2(), info.getLack()));
        iCreator.setHashtable(info);
        iCreator.setWhichMatNr(i);
        img = iCreator.createImage(false);
        if(i == 1)
            //here i would like to start showing the first image
            display.showImage(img);
      //thats an older version where i displayed both images after they had been
      //created.
      //Thread t = new Thread(new ImageDisplay(scanField.getText(), this));
      //t.start();
      //here i would like to show the second image.
      display.showImage(img);
      scanField.setText("");
    else
       doSomethingElse();
    }I hope you can help me.
Thanks!

Answer 1

All actual drawing opertations should occur on the dispatcher thread. When the first image is ready you could use SwingUtiltiies.invokeLater() to place a task on the dispatcher thread to draw the image e.g.
final BufferedImage img = iCreator.createImage(false);
if(i == 1)
  SwingUtilities.invokeLater(new Runnable() {
     public void run() {
       display.showImage(img);
   });(Both the variables uses in run() must be final.
But it's probably better to have a java.awt.Component of some kind for each image to be displayed, and whose paint method does the actual rendering, if the image is ready (is blank otherwise). Then, when the image is ready you need only call repaint on the components.