code: public static <T> Subscription subscribe(ObservableValue<T> observable, Consumer<? super T> subscriber) {
          subscriber.accept(observable.getValue());
          ChangeListener<? super T> listener = (obs, oldValue, newValue) -> subscriber.accept(newValue);
          observable.addListener(listener);
          return () -> observable.removeListener(listener);
      }
docs: Invokes {@code subscriber} for the current and every new value of
  {@code observable}.
  @param observable observable value to subscribe to
  @param subscriber action to invoke for values of {@code observable}.
  @return a subscription that can be used to stop invoking subscriber
  for any further {@code observable} changes.