How do I show the bottom background to the buttons?

Question

I have two classes, one where I create the frame and all the other things, and the class "RoundedButton", that is extended to JButton, where I modify the buttons in order to make it Rounded. When I run the programme and hover the mouse over the button the bottom background disappears. This is the class RoundedBotton:

public class RoundedButton extends JButton {
private Color backgroundColor;
private Color foregroundColor;
private Color hoverBackgroundColor;

    public RoundedButton(String label, Color backgroundColor, Color foregroundColor) {
        super(label);
        this.backgroundColor = backgroundColor;
        this.foregroundColor = foregroundColor;
        this.hoverBackgroundColor = backgroundColor.darker();
        setBorderPainted(false);
        setBackground(backgroundColor);
        setForeground(foregroundColor);
        addMouseListener(new MouseAdapter() {
            @Override
            public void mouseEntered(MouseEvent e) {
                setBackground(hoverBackgroundColor);
            }
    
            @Override
            public void mouseExited(MouseEvent e) {
                setBackground(backgroundColor);
            }
        });
    }
    
    @Override
    protected void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D) g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        RoundRectangle2D.Float roundRect = new RoundRectangle2D.Float(0, 0, getWidth(), getHeight(), 50, 50);
        g2.clip(roundRect);
        super.paintComponent(g2);
    }
    
    @Override
    protected void paintBorder(Graphics g) {
        g.setColor(backgroundColor);
        g.drawRoundRect(0, 0, getWidth()-1, getHeight()-1, 50, 50);
    }
}

This is the method, where I create the frame and all other stuff:

    void create(){ 
        JFrame f = new JFrame("Rubrica"); 
        f.setSize(600,750); 
        f.setResizable(false);
        Font titFont = new Font("Oswald", Font.PLAIN,35);     //Font per il titolo
        Color bgColor = Color.decode("#333b41");
        Color bColor = Color.decode("#202329");
        Color cancColor = Color.decode("#f42244");
        Color newColor = Color.decode("#2dc05f");
    
        JPanel p = new JPanel(new BorderLayout());
        f.add(p);
        //useless code
        JPanel pButton = new JPanel(new GridLayout(1,2,10,10));
        pButton.setPreferredSize(new Dimension(600,80));
        pButton.setBackground(bColor);
        p.add(pButton, BorderLayout.SOUTH);
    
        RoundedButton insert = new RoundedButton("Insert", newColor, Color.white);
        RoundedButton delete = new RoundedButton("Delete", cancColor, Color.white);
    
        pButton.add(insert);
        pButton.add(delete);
    
        f.setVisible(true);
        f.setDefaultCloseOperation(EXIT_ON_CLOSE);
}

I expect to hover themouse over the buttons and still see the colour of the panel where it is posizionated

Answer 1

So, on MacOS, you're "roll over" workflow doesn't work for me AND, it also paints the focus rectangle, which isn't pretty...

So, instead of doing this...

setBackground(backgroundColor);
setForeground(foregroundColor);
addMouseListener(new MouseAdapter() {
    @Override
    public void mouseEntered(MouseEvent e) {
        setBackground(hoverBackgroundColor);
    }

    @Override
    public void mouseExited(MouseEvent e) {
        setBackground(backgroundColor);
    }
});

I would instead make use of the "roll over" support which already exists and change your class to something more like...

public class RoundedButton extends JButton {
    private Color hoverBackgroundColor;

    public RoundedButton(String label, Color backgroundColor, Color foregroundColor) {
        super(label);
        this.hoverBackgroundColor = backgroundColor.darker();
        
        setBackground(backgroundColor);
        setForeground(foregroundColor);
        setBorderPainted(false);
        setFocusPainted(false);
        setOpaque(false);
        setRolloverEnabled(true);
    }

    @Override
    protected void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D) g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

        ButtonModel model = getModel();

        RoundRectangle2D.Float roundRect = new RoundRectangle2D.Float(0, 0, getWidth(), getHeight(), 50, 50);
        // This kind of thing always freaks me out - but that's me
        //g2.clip(roundRect);
        if (model.isRollover()) {
            g2.setColor(hoverBackgroundColor);
        } else {
            g2.setColor(getBackground());
        }
        g2.fill(roundRect);

        super.paintComponent(g2);
    }

    @Override
    protected void paintBorder(Graphics g) {
        g.setColor(getBackground());
        g.drawRoundRect(0, 0, getWidth() - 1, getHeight() - 1, 50, 50);
    }
}

Oh, and calling setPreferredSize is a really bad idea