title: ObservableValue change listeners: how to access
body: <p>I'm new to JavaFX and have started converting custom components written in Swing. As a best practice I have always checked whether an event listener (PropertyChangeListener, MouseListener, ActionListener etc.) is already included in the target object's listeners to make sure the same listener isn't being added twice. I'm trying to do the same with JavaFX but can't find any way to access the list of listeners (for example, to run a list.contains(listener) check).</p>
  
  <p>Am I looking for something that doesn't exist? If so, is there some good reason why JavaFX doesn't include this feature (IMHO it should)?</p>
  
  <p>Thanks for the feedback!</p>