JComponent child not painting correctly

Question

Okay, I promise this will be my last question for the night. For homework we have to do this card layout thing. The problem I am having is that, even though my Sprites paint function is getting called, the Graphics it is getting set doesn't work (I acctually think it is appearing for a second, then disapearing). Can anyone see what I'm missing?
Thanks everyone.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class mainWindow extends JFrame {
    public mainWindow(){
        super("Pumpkin Viewer");
        setSize(800, 600);
        setVisible(true);
        JPanel card1 = new JPanel();
        card1.add(new Sprite());
        card1.add(new JButton("Button 2"));
        card1.add(new JButton("Button 3"));
        JPanel card2 = new JPanel();
        card2.add(new JTextField("TextField", 20));
        getContentPane().setLayout(new CardLayout());
        getContentPane().add(card1, "First");
        getContentPane().add(card2, "Second");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        addMouseListener(new MouseListener(){
            public void mouseReleased(MouseEvent e){};
            public void mouseClicked(MouseEvent e){
                CardLayout cardLayout = (CardLayout)(getContentPane().getLayout());
                cardLayout.next(getContentPane());
            public void mouseEntered(MouseEvent e){};
            public void mouseExited(MouseEvent e){};
            public void mousePressed(MouseEvent e){};
    public static void main(String[] args) {
        new mainWindow();
    public void paint(Graphics g){
        super.paint(g);
class Sprite extends JComponent{
    public void paint(Graphics g){
        g.fillOval(100, 100, 10, 10);
        g.drawOval(100, 100, 10, 10);
}

Answer 1

I have no idea why setPerferredSize works and setBounds doesn't setBounds will set the "size" and "location" of a component and should only be used when the LayoutManager has been set to null.
The preferred size is used by the Layout Manager to layout the components once the components are layed out the LayoutManager will use setSize() and setLocation and therefore override the previous settings for these methods.
When a component is painted it will use the "size" and "location" of the component.