How do I use thread.sleep or swing timer to delay my algorithm visualizer?

Question

Whenever I use thread.sleep on my algorithm visualizer, my screen turns white. I have tried using a swing timer, but I couldn't do it since I am also trying to run the sorting loop. Other times when I tried to use swing timer, it ran the sorter completely and just infinitely called repaint(). I have also tried creating a new thread and putting thread.sleep onto there, but my screen turned white again. I'm not sure if a swing timer could work in this scenario.

public void drawPanel() {
    ActionListener action = new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            repaint();
            System.out.println("repained");
        }
    };
    timer = new Timer(1000, action);
    timer.setRepeats(false);
    timer.start();
}

public void paintComponent(Graphics g) {
    super.paintComponent(g);
    this.setBackground(Color.darkGray);
    Graphics2D g2d = (Graphics2D) g;
    int width = 10;
    int x = 0;
    Algorithims.HeapSort(listArr);
    for (int i = 0; i < (screenWidth - 15) / width; i++) {
        g2d.setPaint(Color.white);
        g2d.fillRect(x, (screenHeight - listArr[i]) - 40, width, listArr[i]);
        g2d.setPaint(Color.black);
        g2d.drawRect(x, (screenHeight - listArr[i]) - 40, width, listArr[i]);
        x += width;
    }
    
}

public void swap(int i, int j) {
    int temp = listArr[i];
    listArr[i] = listArr[j];
    listArr[j] = temp;
    GUI gui = new GUI();
    gui.drawPanel();
}

public static void main(String[] args) {
    // TODO Auto-generated method stub
    listArr = shuffleRectangles();
    JFrame frame = new JFrame();
    GUI gui = new GUI();
    frame.setTitle("Algorithim Visualizer");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(screenWidth, screenHeight); 
    frame.setResizable(false);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
    frame.add(gui);
    
}

Here is the the sorter from a different class:

public static void HeapSort(int[] array) {
    GUI gui = new GUI();
    for (int i = 0; i < array.length; i++) {
        for (int j = 0; j < array.length; j++) {
            if (array[i] < array[j]) {
                //swapping i and j
                gui.swap(i, j);

            }
        }
    }   
}