JPanel freezes my whole application when trying to draw on it

Question

I am coding Oregon Trail for a school project and I am implementing the hunting mini game. We are using model view presenter with a card layout. When the HuntingPanel gets switched to it calls run, and the JOptionPane comes up, but then the whole application freezes and I have to force quit. I coded the entire hunting game in a separate project, and just now brought the files over to the Oregon Trail game. It works fine in its own project with its own JFrame. I'm not sure what to do.

I call this to initialize the panel, switch to it, and run the game.

    public void initialize(int ammo) {
         player.setBullets(ammo);
         bulletLabel.setText("Bullets: "+player.getBullets());
         presenter.switchToPanel(OregonTrailPresenter.HUNTING_PANEL);
         run();
     }

This is my run method.

public void run() {
    // starting message
    JOptionPane.showMessageDialog(null, "You have reached a nearby field to hunt. You will stay\nhere until " +
            "you run out of ammunition or click Return to Trail.");
    // while the player has bullets or doesn't click return to trail
    while (player.getBullets() > 0 && stillHunting) {
        // creates random animals
        checkForAnimal();
        // moves and updates screen
        repaint();
        update();

        try {
            Thread.sleep(50);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    endHunting();
}

And here are other method used.

private void checkForAnimal() {
    int x = 0;
    int y = rand.nextInt(MAX_Y)-40;
    int rand1 = rand.nextInt(100);
    String str = null;
    if (rand1 < 50) {
        str = "left";
        x = MAX_X-40;
    }
    else if (rand1 >= 50) {
        str = "right";
        x = 0;
    }

    double gen = rand.nextGaussian(); // gen is a number from -inf to +inf
    gen = Math.abs(gen); // gen is now a number from 0 to inf       
    if (gen >= 1.9 && gen < 2.1) { //1.19%
        animalList.add(new Bunny(x,y,str));
    }
    if(gen >= 2.1 && gen < 2.2) {  //0.9%
        animalList.add(new Bear(x,y,str));
    }
    if (gen >= 2.2 && gen < 2.3) { 
        animalList.add(new Deer(x,y,str));
    } 

}

    public void update() {
    for (int i = 0; i < animalList.size(); i++) {
        animalList.get(i).move();
    }
}

Answer 1

You have to implement javax.swing.Timer instead of Thread.sleep(int), because this code line freezes all GUI during EDT until Thread.sleep(int) ends. Here is demonstrations what happens if the GUI is delayed during EDT by Thread.sleep(int)