code: public final Observable<T> max(Comparator<? super T> comparator) {
          return OperatorMinMax.max(o, comparator);
      }
docs: Returns an Observable that emits the maximum item emitted by the source Observable, according to the
  specified comparator. If there is more than one item with the same maximum value, it emits the
  last-emitted of these.
  <p>
  <img width="640" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/max.png" alt="">
  
  @param comparator
  the comparer used to compare items
  @return an Observable that emits the maximum item emitted by the source Observable, according to the
  specified comparator
  @throws IllegalArgumentException
  if the source is empty
  @see <a href="https://github.com/ReactiveX/RxJava/wiki/Mathematical-and-Aggregate-Operators#wiki-max">RxJava Wiki: max()</a>
  @see <a href="http://msdn.microsoft.com/en-us/library/hh211635.aspx">MSDN: Observable.Max</a>