svoid onTabSelected(JTabbedPane tabs, Runnable r) {
  if (tabs != null) swing {
    tabs.getModel().addChangeListener(changeListener(r));
  }
}

svoid onTabSelected(JTabbedPane tabs, IVF1<Int> r) {
  if (tabs != null && r != null)
    onTabSelected(tabs, -> r.get(tabs.getSelectedIndex()));
}