public void registerUrlChangeListener(UrlChangeListener urlChangeListener){
  if (!urlChangeListeners.contains(urlChangeListener)) {
    urlChangeListeners.add(urlChangeListener);
  }
}

public void registerUrlChangeListener ( UrlChangeListener urlChangeListener ) { if ( ! urlChangeListeners . contains ( urlChangeListener ) ) { urlChangeListeners . add ( urlChangeListener ) ; } }
registers the listener for when url changes .
