src/main/java/io/reactivex/Maybe.java
@SuppressWarnings({ "rawtypes", "unchecked" })
    @BackpressureSupport(BackpressureKind.FULL)
    @CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Flowable<T> concatEager(Iterable<? extends MaybeSource<? extends T>> sources) {
        return Flowable.fromIterable(sources).concatMapEager((Function)MaybeToPublisher.instance());
    }
@SuppressWarnings({ "rawtypes", "unchecked" })
    @BackpressureSupport(BackpressureKind.FULL)
    @CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Flowable<T> concatEager(Iterable<? extends MaybeSource<? extends T>> sources) {
        return Flowable.fromIterable(sources).concatMapEager((Function)MaybeToPublisher.instance());
    }
Concatenates a sequence of MaybeSources eagerly into a single stream of values.
<p>
Eager concatenation means that once a subscriber subscribes, this operator subscribes to all of the
source MaybeSources. The operator buffers the values emitted by these MaybeSources and then drains them
in order, each one after the previous one completes.
<p>
<img width="640" height="526" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.concatEager.i.png" alt="">
<dl>
<dt><b>Backpressure:</b></dt>
<dd>Backpressure is honored towards the downstream.</dd>
<dt><b>Scheduler:</b></dt>
<dd>This method does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
@param <T> the value type
@param sources a sequence of MaybeSource that need to be eagerly concatenated
@return the new Flowable instance with the specified concatenation behavior