protected Container createMessageArea() 
{
        JPanel top = new JPanel();
        top.setName("OptionPane.messageArea");
        top.setLayout(new BorderLayout());
        /* Fill the body. */
        Container          body = new JPanel(new GridBagLayout());
        Container          realBody = new JPanel(new BorderLayout());
        body.setName("OptionPane.body");
        realBody.setName("OptionPane.realBody");
        if (getIcon() != null) {
            JPanel sep = new JPanel();
            sep.setName("OptionPane.separator");
            sep.setPreferredSize(new Dimension(15, 1));
            realBody.add(sep, BorderLayout.BEFORE_LINE_BEGINS);
        }
        realBody.add(body, BorderLayout.CENTER);
        GridBagConstraints cons = new GridBagConstraints();
        cons.gridx = cons.gridy = 0;
        cons.gridwidth = GridBagConstraints.REMAINDER;
        cons.gridheight = 1;
        SynthContext context = getContext(optionPane, ENABLED);
        cons.anchor = context.getStyle().getInt(context,
                      "OptionPane.messageAnchor", GridBagConstraints.CENTER);
        context.dispose();
        cons.insets = new Insets(0,0,3,0);
        addMessageComponents(body, cons, getMessage(),
                          getMaxCharactersPerLineCount(), false);
        top.add(realBody, BorderLayout.CENTER);
        addIcon(top);
        return top;
}

Messaged from installComponents to create a Container containing the body of the message. The icon is the created by calling addIcon.

 protected Container createSeparator() 
{
        JSeparator separator = new JSeparator(SwingConstants.HORIZONTAL);
        separator.setName("OptionPane.separator");
        return separator;
}

 public static ComponentUI createUI(JComponent x) 
{
        return new SynthOptionPaneUI();
}

Creates a new BasicOptionPaneUI instance.

 public SynthContext getContext(JComponent c) 
{
        return getContext(c, getComponentState(c));
}

 protected boolean getSizeButtonsToSameWidth() 
{
        return DefaultLookup.getBoolean(optionPane, this,
                                        "OptionPane.sameSizeButtons", true);
}

 protected  void installComponents() 
{
        optionPane.add(createMessageArea());
        Container separator = createSeparator();
        if (separator != null) {
            optionPane.add(separator);
            SynthContext context = getContext(optionPane, ENABLED);
            optionPane.add(Box.createVerticalStrut(context.getStyle().
                       getInt(context, "OptionPane.separatorPadding", 6)));
            context.dispose();
        }
        optionPane.add(createButtonArea());
        optionPane.applyComponentOrientation(optionPane.getComponentOrientation());
}

 protected  void installDefaults() 
{
        updateStyle(optionPane);
}

 protected  void installListeners() 
{
        super.installListeners();
        optionPane.addPropertyChangeListener(this);
}

 public  void paint(Graphics g,
    JComponent c) 
{
        SynthContext context = getContext(c);
        paint(context, g);
        context.dispose();
}

 protected  void paint(SynthContext context,
    Graphics g) 
{

}

 public  void paintBorder(SynthContext context,
    Graphics g,
    int x,
    int y,
    int w,
    int h) 
{
        context.getPainter().paintOptionPaneBorder(context, g, x, y, w, h);
}

 public  void propertyChange(PropertyChangeEvent e) 
{
        if (SynthLookAndFeel.shouldUpdateStyle(e)) {
            updateStyle((JOptionPane)e.getSource());
        }
}

 protected  void uninstallDefaults() 
{
        SynthContext context = getContext(optionPane, ENABLED);
        style.uninstallDefaults(context);
        context.dispose();
        style = null;
}

 protected  void uninstallListeners() 
{
        super.uninstallListeners();
        optionPane.removePropertyChangeListener(this);
}

 public  void update(Graphics g,
    JComponent c) 
{
        SynthContext context = getContext(c);
        SynthLookAndFeel.update(context, g);
        context.getPainter().paintOptionPaneBackground(context,
                          g, 0, 0, c.getWidth(), c.getHeight());
        paint(context, g);
        context.dispose();
}