How do I invoke an immediate update to a Java GUI? (conflict with Thread.sleep())

Question

I am making the game Memory, when you pick two cards and if they match you get to keep them, otherwise you turn them back. If you then remember cards you have already chosen, you can venture a better guess on the next two cards.

The problem I have involves the repaint() method not immediately repainting.

When I flip the second card, no matter the outcome, I want to show both cards flipped right-side up before either discarding them or flipping them back over. I do this by calling sleep().

Of course if I repaint() the cards to flip them right-side up, wait a second, and then repaint() again based on their values, helpful little Java will only repaint once (I miss C!).

Basically I want to force invoke a update before I sleep(). I have read some other threads that basically say the best way is to create two threads to keep your logic and graphics separate, and then you can sleep() your logic and keep your GUI updating, but I am in the first semester of a first year CS course in high school, and I would want to keep it on the course's level (although I spent quite a bit of time over the summer web developing and coding in C).

Because I know the helpful folks on StackOverflow love to read code, here is the part of the program I am referring to below. The class HitArea is the Card object and the cards[] array contains an amount of HitArea's.(I haven't gotten to renaming the HitArea class). activeCard1 and activeCard2 are HitArea instances I use to keep track of the user's two selections, and the blank constructor is a reserved "invisible" HitArea, although I will change it to null later. Finally, cards.flip() inverts a toggle boolean which determines whether the card is right-side up.

public void respond(HitArea choice)
{
    if(choice.inGame)
    {
        if(activeCard1.value == 0 && activeCard1.value == 0)
            activeCard1 = choice;
        else if((!(activeCard1.value == 0) && activeCard2.value == 0) && (activeCard1.id != choice.id))
        {
            activeCard2 = choice;
            check();
        }

    }
}
public void check()
{
    update();
    pause(250);
    if(activeCard2.value == activeCard1.value)
    {
        score += 2;
        activeCard1.inGame = false;
        activeCard2.inGame = false;
    }
    activeCard1.flip();
    activeCard2.flip();
    activeCard1 = new HitArea();
    activeCard2 = new HitArea();
}
public void pause(int milliseconds)
{
    try{
      Thread.currentThread().sleep(milliseconds);
    }
    catch(InterruptedException e){
        System.out.println("Exception: " + e);
    }
}

public void mousePressed(MouseEvent e)
{
    int x = e.getX();
    int y = e.getY();

    for (int i = 0; i < cardNum; i++)
        if(cards[i].boundsCheck( x, y ) )
        {
            repaint();
            cards[i].flip();
            respond(cards[i]);
        }
}

I have no doubt there are some issues in my code, so feel free to point them out. I think my basic structure is okay, and I would rather not create multiple threads for this project (remember, it's basic!).

Scherman

Answer 1

Don't call Thread.sleep(...) on the main Swing thread, the EDT. Ever. Instead use a Swing Timer.

Consider using JLabels to display your images, and then you could "flip" your cards by simply swapping out ImageIcons. When the second card has been flipped, if there's no match, start a non-repeating Swing Timer with a delay for xxxx ms, and in the Timer's ActionListener's actionCommand method have it revert both JLabel's back to the default ImageIcon.

The javax.swing.Timer tutorial can be found here: How to use Swing Timers

Edit:
Regarding your comment about using g.drawString: it's even easier now since all you have to do is swap out your JLabel's text. But later if you decide to upgrade the program to display images, you've got it all set to do this.

Edit 2:
Regarding your question about making a new ActionListener class: I'd use an anonymous inner class for this. For example:

  int delayTime = 2 * 1000;
  javax.swing.Timer myTimer = new Timer(delayTime, new ActionListener() {

     @Override
     public void actionPerformed(ActionEvent e) {
        // TODO: put in the code you want called in xxx mSecs.
     }
  });
  myTimer.setRepeats(false);
  myTimer.start();

Notus

I would bold and italicize "Ever". :) – Lenni

I am just display some g.drawString(...) text, no images. Would the same apply? – Scherman

As I understand, I need to make a new ActionListener class? How would I do that?download.oracle.com/javase/1.4.2/docs/api/javax/swing/… – Scherman

@EricThoma: Please see Edit 2 to my answer above. – Notus

@HovercraftFullOfEels, but, wouldn't SwingTimer also invoke Thread.sleep for it's delay parameter? What if people rather want to sleep the EDT itself? Or is it like..., pause the operation in worker thread and pass the result to EDT? – Esque

@Plain_Dude_Sleeping_Alone: yes, a Swing Timer likely does call Thread.sleep but off of the EDT. As noted in my answer, you never want to call Thread.sleep on the EDT since that makes the GUI completely non-responsive -- you can't even close it by clicking on the OS's close button on the right upper corner of the top-level window. If you want to pause GUI code flow in a section of code, then consider using a modal dialog such as a JOptionPane. – Notus