JLabel图形在错误的时间更改

Question

I have a slot machine program with some graphics, and the graphic is supposed to change when you pull the lever and for some reason it changes the graphic after it goes through all of the other code first. Have a look:

Declare images:

static ImageIcon jImage = new ImageIcon("C:\\Users\\Harry\\Desktop\\jackpotLeverNotPulled.png");
static ImageIcon jackpot1 = new ImageIcon("C:\\Users\\Harry\\Desktop\\jackpotimage1.png");
static ImageIcon jackpotPulled = new ImageIcon("C:\\Users\\Harry\\Desktop\\jackpotLeverPulled.png");

Now I add to panel:

static JLabel jlb = new JLabel(jImage);

Now I want the image to change when a certain area is clicked on my panel but the main jackpot code runs first and then the image changes:

public void mousePressed(MouseEvent e) {

        // Returns the X coordinate of where the mouse was click on the panel
        System.out.println("X Coordinate: " + e.getX() );


        //  Returns the Y coordinate of where the mouse was click on the panel
        System.out.println("Y Coordinate: " + e.getY() );    
        System.out.println();

        Scanner ansr = new Scanner(System.in);
        String yesno;

        int random =  (int)(Math.random() * 21 );
        int percentCheck =  (int)(Math.random() * 10 );

        if (e.getX ()>975 && e.getX ()<1159 && e.getY ()>82 && e.getY ()<218){
            jlb.setIcon(jackpotPulled);
            if (cashMoneyz<1) {

                System.out.println("Insufficient funds");
                image1.setIcon(jackpot1);
            } else {

                System.out.println("One dollar has been removed from you slot machine balance");
                cashMoneyz--;
                try {
                    System.out.println("Spinning...");
                    Thread.sleep(1000);
                    System.out.println("Spinning...");
                    Thread.sleep(1000);
                    System.out.println("SPINNINGGGGG...OMG SOOO INTENSE");
                    Thread.sleep(1000);
                } catch (InterruptedException ie)
                {
                }

            }   
            System.out.println("You have this much money (in dollars) left in your slot machine balance: " + cashMoneyz);
            System.out.println("");
            System.out.println("----------------------------------------------------------------------------------");
        }

It does the if statements and try catches and only changes the graphic to jackpotPulled at the end of everything. Thanks in advance :)

Answer 1

There are basically 2 problems in your code:

1) A call to label.setImage() won't update immediately, as this is true for everything in AWT and Swing. Any time a repaint request is fired, it is simply added to a repaint queue, that will wait patiently for all other tasks done in the EDT (Event Dispatching Thread) to finish. But since you do other things in the mousePressed() , they will run first. A simple solution for this would be to do the computing in mouseReleased() . But a bigger problem exists.

2) What you are currently doing is "starving" the EDT - a bad programming practice - as all screen related invocations must be executed immediately. Sleeping the EDT won't allow any repaints to take place while running. This is true for any long running tasks as well. Its solution is to run the non-painting calls in a different thread:

private volatile boolean isComputing = false;

public void mousePressed(MouseEvent evt) {
    if(isComputing)
        return;
    isComputing = true;

    // .
    // .
    // .
    // change icon here, or any
    // other swing related change.
    // .
    // .

    // run game
    new Thread(){
        public void run(){
           // all non-swing computations

           SwingUtilities.invokeLater(new Runnable() {
               public void run() {
                   // change back icons,
                   // and some other swing updates
               }
           }
           isComputing = false;
        }
    }.start();
}

Answer 2

An event handler ( mousePressed ) souldn't take a long time to complete, there should be no sleep s in it. As long as it runs (or sleeps), nothing else can happen. The runtime is waiting for the handler to return and displays the image after that. I would move most of the code to a function called by a timer, and use a state variable to keep track of how intensely the wheels are spinning.