code: @CheckReturnValue
      @BackpressureSupport(BackpressureKind.PASS_THROUGH)
      @SchedulerSupport(SchedulerSupport.NONE)
      @GwtIncompatible("Class.isInstance")
      public final <U> Flowable<U> ofType(final Class<U> clazz) {
          ObjectHelper.requireNonNull(clazz, "clazz is null");
          return filter(Functions.isInstanceOf(clazz)).cast(clazz);
      }
docs: Filters the items emitted by a Publisher, only emitting those of the specified type.
  <p>
  <img width="640" height="310" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/ofClass.png" alt="">
  <dl>
  <dt><b>Backpressure:</b></dt>
  <dd>The operator doesn't interfere with backpressure which is determined by the source {@code Publisher}'s backpressure
  behavior.</dd>
  <dt><b>Scheduler:</b></dt>
  <dd>{@code ofType} does not operate by default on a particular {@link Scheduler}.</dd>
  </dl>
  
  @param <U> the output type
  @param clazz
  the class type to filter the items emitted by the source Publisher
  @return a Flowable that emits items from the source Publisher of type {@code clazz}
  @see <a href="http://reactivex.io/documentation/operators/filter.html">ReactiveX operators documentation: Filter</a>