public void addListener(@NotNull ConfigurationListener listener){
  if (myListeners == null) {
    myListeners=new ArrayList<>();
  }
  myListeners.add(listener);
}

public void addListener ( @ NotNull ConfigurationListener listener ) { if ( myListeners == null ) { myListeners = new ArrayList < > ( ) ; } myListeners . add ( listener ) ; }
adds a listener to be notified when the configuration changes
