Painted content invisible while resizing in Java

For reference, here is the same program using Swing. Because JPanel is double buffered, it doesn’t flicker as the mouse is released after resizing.

import java.awt.*;
import java.awt.event.*;
import java.util.Random;
import javax.swing.*;

public class SwingPaint {

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.add(new CirclePanel());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setVisible(true);
    }

    private static class CirclePanel extends JPanel {

        private static final Random r = new Random();

        public CirclePanel() {
            this.setPreferredSize(new Dimension(320, 240));
            this.setForeground(new Color(r.nextInt()));
            this.addMouseListener(new MouseAdapter() {

                @Override
                public void mousePressed(MouseEvent e) {
                    CirclePanel.this.update();
                }
            });
        }

        public void update() {
            this.setForeground(new Color(r.nextInt()));
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            Dimension size = this.getSize();
            int d = Math.min(size.width, size.height) - 10;
            int x = (size.width - d) / 2;
            int y = (size.height - d) / 2;
            g.fillOval(x, y, d, d);
            g.setColor(Color.blue);
            g.drawOval(x, y, d, d);
        }
    }
}