code: public static <T> Observable<T> doWhile(Observable<? extends T> source, Func0<Boolean> postCondition) {
          return Observable.create(new OperatorWhileDoWhile<T>(source, TRUE, postCondition));
      }
docs: Return an Observable that replays the emissions from the source
  Observable, and then continues to replay them so long as a condtion is
  true.
  <p>
  <img width="640" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/doWhile.png" alt="">
  
  @param postCondition
  the post condition to test after the source
  Observable completes
  @return an Observable that replays the emissions from the source
  Observable, and then continues to replay them so long as the post
  condition is true