static <A extends JComponent> A onClick(final A c, fO runnable) {
  if (c != null) swing {
    c.addMouseListener(new MouseAdapter {
      public void mouseClicked(MouseEvent e) {
        callF(runnable, e);
      }
    });
  }
  ret c;
}

// re-interpreted for buttons
static void onClick(JButton btn, final O runnable) {
  onEnter(btn, runnable);
}