public JApplet() throws HeadlessException 
{
        setLayout(new BorderLayout());
        setRootPaneCheckingEnabled(true);
        setRootPane(createRootPane());
        setLocale(JComponent.getDefaultLocale());
        setBackground(Color.white);
        // enable events
        enableEvents(AWTEvent.KEY_EVENT_MASK);
        setFocusTraversalPolicyProvider(true);
        setFocusTraversalPolicy(KeyboardFocusManager.getCurrentKeyboardFocusManager()
                .getDefaultFocusTraversalPolicy());
}

 protected  void addImpl(Component comp,
    Object constraints,
    int index) 
{
        if (isRootPaneCheckingEnabled()) {
            getContentPane().add(comp, constraints, index);
            return;
        }
        super.addImpl(comp, constraints, index);
}

 protected JRootPane createRootPane() 
{
        return new JRootPane();
}

 public AccessibleContext getAccessibleContext() 
{
        if (accessibleContext == null) {
            accessibleContext = new AccessibleJApplet();
        }
        return accessibleContext;
}

 public Container getContentPane() 
{
        return getRootPane().getContentPane();
}

 public Component getGlassPane() 
{
        return getRootPane().getGlassPane();
}

 public JMenuBar getJMenuBar() 
{
        return getRootPane().getJMenuBar();
}

 public JLayeredPane getLayeredPane() 
{
        return getRootPane().getLayeredPane();
}

 public JRootPane getRootPane() 
{
        return rootPane;
}

 protected boolean isRootPaneCheckingEnabled() 
{
        return rootPaneCheckingEnabled;
}

 public  void remove(Component comp) 
{
        if (comp == getRootPane()) {
            // remove directly from JApplet
            super.remove(comp);
        } else {
            getContentPane().remove(comp);
        }
}

 public  void setContentPane(Container contentPane) 
{
        getRootPane().setContentPane(contentPane);
}

 public  void setGlassPane(Component glassPane) 
{
        getRootPane().setGlassPane(glassPane);
}

 public  void setJMenuBar(JMenuBar menuBar) 
{
        getRootPane().setJMenuBar(menuBar);
}

 public  void setLayeredPane(JLayeredPane layeredPane) 
{
        getRootPane().setLayeredPane(layeredPane);
}

 public  void setLayout(LayoutManager layout) 
{
        if (isRootPaneCheckingEnabled()) {
            getContentPane().setLayout(layout);
        } else {
            super.setLayout(layout);
        }
}

 protected  void setRootPane(JRootPane root) 
{
        if (rootPane != null) {
            remove(rootPane);
        }
        rootPane = root;
        if (root != null) {
            super.addImpl(root, null, 0);
        }
}

 protected  void setRootPaneCheckingEnabled(boolean enabled) 
{
        rootPaneCheckingEnabled = enabled;
}

 public  void update(Graphics g) 
{
        paint(g);
}

Just calls paint(g). This method was overridden to prevent an unnecessary call to clear the background.