code: public void handleStateEvent(String callbackKey) {
          if (handlers.containsKey(callbackKey) && handlers.get(callbackKey) instanceof StateEventHandler) {
              ((StateEventHandler) handlers.get(callbackKey)).handle();
          } else {
              System.err.println("Error in handle: " + callbackKey + " for state handler ");
          }
      }
docs: This method is called from Javascript, passing in the previously created
  callback key. It uses that to find the correct handler and then passes on
  the call. State events in the Google Maps API don't pass any parameters.
  
  @param callbackKey Key generated by the call to registerHandler.