How do you repaint a container immediately as components are added in a separate thread in JAVA?

Question

I am using java. I have a click event that adds "squares" to a container, in a loop. I want each square to show up RIGHT when it is added. I tried running the 'adding of the squares' in a separate thread, but it is not working.

Here is some code I use for 'public class GuiController implements ActionListener, MouseListener':

@Override
public void mouseClicked(MouseEvent e)
{
    //createBoardPane();
    new Thread
    (
        new Runnable() 
        {
            public void run() 
            {
                showAnimation();
            }
        }
    ).start();
}

public void showAnimation()
{   
    for(int i = 0; i < model.getAnimationList().size(); i++)
    {
        String coord = model.getAnimationList().get(i);
        int x = Integer.parseInt(coord.substring(0, coord.indexOf(',')));
        int y = Integer.parseInt(coord.substring(coord.indexOf(',') + 1, coord.length() - 2));
        boolean shouldPlacePiece = (coord.charAt(coord.length() - 1) == 'p');

        if(shouldPlacePiece)
        {
            model.getView().getBoardPane().getComponent(x + (y * model.getBoardSize())).setBackground(Color.BLACK);
        }
        else
        {
            model.getView().getBoardPane().getComponent(x + (y * model.getBoardSize())).setBackground(Color.WHITE);
        }

        model.getView().getBoardPane().repaint();

        long time = System.currentTimeMillis();
        while((System.currentTimeMillis() - time) < 250)
        {
            // wait loop
        }
    }
}

any help is appreciated!

Answer 1

Creating a separate Thread to run for this longish-running task was an excellent idea - unless you want to lock-up interactions with your GUI while doing your animation.

Now, Swing GUI objects are not Thread safe (with few exceptions), so you cannot work with them from a thread other than Swing's Event Dispatch Loop's thread. So take all the GUI update code in your for-loop, and wrap it with a new Runnable (yes, another one). Then call SwingUtilities.invokeLater(Runnable doRun) with that Runnable on each iteration of the loop.

Your GUI update code will then be scheduled to run ASAP on the Event Dispatch Loop, which will occur while your worker thread goes to sleep (do you have anything against Thread.sleep?).

Alternative: Use SwingWorker instead of Thread

SwingWorker will create and manage a new the Thread for you, and publish data that it (SwingWorker) will cause to be run on the Event Dispatch Loop's thread. You'll override doInBackground with your code. Call publish with parameters to push across into the Event Dispatch Thread. Override process with code to process those parameters and update your GUI.

On gotcha with SwingWorker is that it accumulates published events over a period of about 33 milliseconds. If you're publishing more frequent than that you may get all your events bunched together every 33 milliseconds or so. In you case, 250 milliseconds between updates shouldn't be a problem.