svoid onUpdate(JComponent c, Runnable r) {
  onUpdate(c, (O) r);
}

// legacy signature
svoid onUpdate(JComponent c, O r) {
  if (c cast JTextComponent)
    c.getDocument().addDocumentListener(runnableToDocumentListener(r));
  else if (c cast ItemSelectable) // JCheckBox and others
    c.addItemListener(new ItemListener {
      public void itemStateChanged(ItemEvent e) {
        pcallF(r);
      }
    });
  else if (c cast JSpinner)
    onChange(c, r);
  else
    print("Warning: onUpdate doesn't know " + getClassName(c));
}

static void onUpdate(L<? extends JComponent> l, O r) {
  for (JComponent c : l)
    onUpdate(c, r);
}