在java gui swift的2个按钮之间画线，它工作但不准确

I have this simple code:

我有这个简单的代码:

class Success extends JFrame {

    public JButton button1;
    public JButton button2;

    public Success() {
        JPanel panel = new JPanel();
        getContentPane().add(panel);
        setSize(600, 800);

        button1 = new JButton("press");
        button2 = new JButton("this");
        button1.setBounds(100, 200, 100, 100);
        button2.setBounds(400, 500, 100, 100);

        panel.add(button1);
        panel.add(button2);
        panel.setLayout(null);
    }

    public void paint(Graphics g) {
        super.paint(g);  
        Graphics2D g2 = (Graphics2D) g;
        g2.drawLine(button1.getX(), button1.getY(), button2.getX(), button2.getY());
    }

    public static void main(String []args) {
        Success s = new Success();
        s.setVisible(true);
    }
}
class S