src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Observable<T> concatArrayEager(ObservableSource<? extends T>... sources) {
        return concatArrayEager(bufferSize(), bufferSize(), sources);
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Observable<T> concatArrayEager(ObservableSource<? extends T>... sources) {
        return concatArrayEager(bufferSize(), bufferSize(), sources);
    }
Concatenates an array of ObservableSources eagerly into a single stream of values.
<p>
<img width="640" height="410" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/concatArrayEager.png" alt="">
<p>
Eager concatenation means that once a subscriber subscribes, this operator subscribes to all of the
source ObservableSources. The operator buffers the values emitted by these ObservableSources and then drains them
in order, each one after the previous one completes.
<dl>
<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 an array of ObservableSources that need to be eagerly concatenated
@return the new ObservableSource instance with the specified concatenation behavior
@since 2.0