Help animating with SwingWorker

Question

I have an animation on a JPanel. Right now, I am using a Thread, and updating the GUI with
//code for updating variables and such
mazeDisplay.repaint(); //update the JPanel
Thread.sleep(500);// wait for next frame of animationI was told that this was an improper way to do an animation in swing, because using a Thread like this can cause errors. So, I am supposed to use the SwingWorker class, I think.
I am confused with how to use it, though. The doInBackground() method has a return type, but I want it to be void. I have no use for a return type here, as all I am doing is updating a JPanel. Also, I don't know how to pause the thread with something akin to Thread.sleep(). Without that, how am I supposed to wait between frames of the animation?
I looked at the Timer class, but it didn't seem to have what I want either. I only want to update the JPanel when I need to, not at set intervals.
I think I need to use both classes, with SwingWorker doing all the calculations and then creating timers, which exist only to wait the 500ms and then send an ActionEvent that updates the JPanel. Is this right?

Answer 1

My method that solves and animates the maze (this is what the JPanel is displaying) will sometimes update the GUI, and sometimes not. This is because it has a case where the position in the maze does not move. I only update the the maze if the position has moved, otherwise the animation appears inconsistent. That is why I cannot update the GUI on each execution of my animation method, and I only want to update the maze after the animation method has finished calculating a new position.
Here is the working (but improper?) code I had before, maybe it will help you understand:
            //from ActionPerformed method     
            else if (theEventer == toggleAnimate)
                if (animating)                    
                    running.interrupt();                
                else
                    animating = true;                   
                    nextButton.setEnabled(false);
                    prevButton.setEnabled(false);
                    toggleSolution.setEnabled(false);
                    toggleAnimate.setText("Cancel");
                    running = new MazeAnimating();
                    running.start();
                }//end else 
            }//end else if 
class MazeAnimating extends Thread
        char[][] sol;
        int x;
        int y;
        public void run()
            sol = new char[theMaze.getMazeData().length][theMaze.getMazeData()[0].length];                  
            for (int i = 0; i < sol.length; i++)          
                for (int i2 = 0; i2 < sol.length; i2++)
sol[i][i2] = theMaze.getMazeData()[i][i2];
x = theMaze.getStartX();
y = theMaze.getStartY();
mazeDisplay.loadMaze(sol, x, y, theMaze.getEndX(), theMaze.getEndY());
mazeDisplay.setDude(x, y, 0);
mazeDisplay.setDudeVisible(true);
try
if (!solve(0, 0))
mazeDisplay.setDudeExpression(3);
}//end try
catch (InterruptedException e)
}//end catch
finally
solutionShowing = true;
animating = false;
if (mazeIndex < theMazes.size() - 1)
nextButton.setEnabled(true);
if (mazeIndex > 0)
prevButton.setEnabled(true);
toggleSolution.setEnabled(true);
toggleSolution.setText("Revert");
toggleAnimate.setText("Animate");
EventQueue.invokeLater(new Runnable() {
public void run() {
theWindow.pack(); } } );
}//end finally
}//end run
/*Solve the maze*/
//i wont show the calculations, because that is a programming assignment. but, there are three different cases where I update the maze
private boolean solve(int dX, int dY) throws InterruptedException
//there are four cases here
//one where the position is not moved, and the JPanel is not updated
//one where the position is advanced, but the method is still not done executing
//two where the position is changed and the method is done
mazeDisplay.repaint();
return true;
mazeDisplay.repaint();
Thread.sleep(500);
mazeDisplay.repaint();
Thread.sleep(500);
return false;
}//end solve
}//end class MazeAnimating