code: synchronized void addInterestedByClass(Class<?> clazz, Collection<ProbeListener> newListeners) {
          Set<ProbeListener> currentListeners = listenersByClass.get(clazz);
          if (currentListeners == null) {
              currentListeners = new HashSet<ProbeListener>();
              listenersByClass.put(clazz, currentListeners);
          }
          currentListeners.addAll(newListeners);
      }
docs: Associate the collection of listeners with {@link ProbeFilter}s that
  match the specified class with the specified class.
  
  @param clazz the probe source candidate
  @param newListeners listeners with filters that match {@code clazz}