Painting to a JFrame

public class Display{
    JFrame frame;
    JPanel contentPane;
    public Display()
    {
        frame = new JFrame("Painting example"); //initialize JFrame
        contentPane = new JPanel();
        contentPane.setBorder(BorderFactory.createEmptyBorder(20,20,20,20));
        contentPane.setLayout(new GridLayout(1,0));

        panel.setContentPane(contentPane);  // Add content pane to frame
        contentPane.add(new MyPanel()); //Add paint surface
    }
    public static void main(String[] args)
    {
        Display g1 = new Display();
    }
}
class MyPanel extends JPanel{
    public MyPanel() {
            setBorder(BorderFactory.createLineBorder(Color.black));
        }

        public Dimension getPreferredSize() {
            return new Dimension(250,200);
        }

        public void paintComponent(Graphics g) {
            super.paintComponent(g);
// You can add paint objects here or implement double/triple buffering and access it from your main class(es)
            g.setColor(Color.BLACK);
            g.fillRect(0, 0, 1000, 1000);
            g.setColor(Color.RED);
            g.fillOval(100, 100, 10, 10);
        }
}