// c = JComponent or something implementing swing()
static JComponent wrap(O swingable) {
  if (swingable == null) null;
  JComponent c = cast swingable instanceof JComponent ? swingable : callOpt(swingable, "swing");
  if (c instanceof JTable || c instanceof JList
    || c instanceof JTextArea || c instanceof JEditorPane
    || c instanceof JTextPane || c instanceof JTree)
    ret jscroll(c);
  ret c;
}