Java function works only in a standalone call, but not when called by JButton ActionEvent

Question

I have a Bubble Sort algorithm which I want to visualize with SWING in a JFrame. It goes well, if I call the function in a standalone position, but doesn't if I call it from a JButton's ActionListener. (Actually it works, only it doesn't render the array continously - as it should and does in the other case - only in the beginning and the end of the sorting.) Any idea why?

GUI and Main class:

public class sortings {
    
    public static void main(String[] args) {
        
        //create, fill up and print array of 100 elements
        int[] arr = new int[100];
        
        for (int i=0; i<100; i++) {
            int element = ThreadLocalRandom.current().nextInt(1, 100);
            arr[i] = element;
        }
        
        for (int i=0; i<arr.length; i++) {
            System.out.print(arr[i] + ",");
        }
        
        //set up GUI
        Frame frame = new Frame();
        JPanel menuPanel = new JPanel();
        JButton button = new JButton("sort");
        
        Container contentPane = frame.getContentPane();
        contentPane.setPreferredSize(new Dimension(600, 450));
        frame.setLayout(new GridLayout(2,1));
        
        menuPanel.setSize(600, 50);
        menuPanel.add(button);
        
        BubbleSort bs = new BubbleSort(arr);
        
        frame.add(menuPanel);
        frame.add(bs);
        frame.pack();
        
        button.addActionListener((ActionEvent e) -> {
            bs.bubbleSort(); // <- if called from here it renders the array only in the beginning and the end of sorting
        });
        
        bs.bubbleSort(); // <- if called from here it renders the array during sorting continously, as it should
               
        //BubbleSort bs = new BubbleSort(arr);
        //bs.bubbleSort();
    }
}

BubbleSort class and method:

public class BubbleSort extends JPanel {
    
    int[] arr;
    
    public BubbleSort(int[] arr) {
        setSize(600, 400);
        this.arr = arr;
    }
    
    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        for (int i = 0; i < this.arr.length; i++) {
            g.drawLine(i*2+50,50, i*2+50, 50+this.arr[i]);
        }
    }
    
    public void bubbleSort() {
            
        int temp;
        
        for (int i=0; i < 100; i++) {
            for (int j=0; j < this.arr.length-1; j++) {
                if (this.arr[j] < this.arr[j+1]) {
                    temp = this.arr[j];
                    this.arr[j] = this.arr[j+1];
                    this.arr[j+1] = temp;
                    
                    try
                    {
                        Thread.sleep(5);
                    }
                    catch(InterruptedException ex)
                    {
                        Thread.currentThread().interrupt();
                    }
                    
                    repaint();
                }
            }
        }
    }
}