public void showArrows(
  TopicLabel focus, 
  Collection<String> broaderIDs,
  Collection<String> narrowerIDs
) {
  for (Component t : this.getComponentsInLayer(TOPICS_LAYER)) {
    String id = ((TopicLabel) t).getID();
    if (narrowerIDs.contains(id)) {
      this.showArrow(focus, (TopicLabel) t);
    } else if (broaderIDs.contains(id)) {
      this.showArrow((TopicLabel) t, focus);
    }
  }
}