src/main/java/io/reactivex/Observable.java
@SuppressWarnings({ "unchecked" })
    @CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Observable<T> concatArrayDelayError(ObservableSource<? extends T>... sources) {
        if (sources.length == 0) {
            return empty();
        } else
        if (sources.length == 1) {
            return (Observable<T>)wrap(sources[0]);
        }
        return concatDelayError(fromArray(sources));
    }
@SuppressWarnings({ "unchecked" })
    @CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Observable<T> concatArrayDelayError(ObservableSource<? extends T>... sources) {
        if (sources.length == 0) {
            return empty();
        } else
        if (sources.length == 1) {
            return (Observable<T>)wrap(sources[0]);
        }
        return concatDelayError(fromArray(sources));
    }
Concatenates a variable number of ObservableSource sources and delays errors from any of them
till all terminate.
<p>
<img width="640" height="290" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/concatArray.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code concatArrayDelayError} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
@param sources the array of sources
@param <T> the common base value type
@return the new Observable instance
@throws NullPointerException if sources is null