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

// legacy signature
svoid onUpdate(JComponent c, O r) {
  if (c instanceof JTextComponent)
    ((JTextComponent) c).getDocument().addDocumentListener(new DocumentListener() {
      public void insertUpdate(DocumentEvent e) {
        call(r);
      }
      public void removeUpdate(DocumentEvent e) {
        call(r);
      }
      public void changedUpdate(DocumentEvent e) {
        call(r);
      }
    });
  else if (c instanceof ItemSelectable) // JCheckBox and others
    ((ItemSelectable) c).addItemListener(new ItemListener() {
      public void itemStateChanged(ItemEvent e) {
        call(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);
}