static JComboBox centerComboBox(JComboBox cb) swing {
  if (cb != null)
    if (!cb.isEditable()) {
      var r = cb.getRenderer();
      if (!r instanceof CenteredComboBoxRenderer)
        cb.setRenderer(new CenteredComboBoxRenderer(r));
    } else
      centerTextField(textFieldFromComboBox(cb));
  ret cb;
}