code: public static <R> Observable<R> ifThen(Func0<Boolean> condition, Observable<? extends R> then,
              Observable<? extends R> orElse) {
          return Observable.create(new OperatorIfThen<R>(condition, then, orElse));
      }
docs: Return an Observable that emits the emissions from one specified
  Observable if a condition evaluates to true, or from another specified
  Observable otherwise.
  <p>
  <img width="640" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/ifThen.e.png" alt="">
  
  @param <R>
  the result value type
  @param condition
  the condition that decides which Observable to emit the
  emissions from
  @param then
  the Observable sequence to emit to if {@code condition} is {@code true}
  @param orElse
  the Observable sequence to emit to if {@code condition} is {@code false}
  @return an Observable that mimics either the {@code then} or {@code orElse} Observables depending on a condition function