src/main/java/io/reactivex/Completable.java
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public static Completable mergeArray(CompletableSource... sources) {
        ObjectHelper.requireNonNull(sources, "sources is null");
        if (sources.length == 0) {
            return complete();
        } else
        if (sources.length == 1) {
            return wrap(sources[0]);
        }
        return RxJavaPlugins.onAssembly(new CompletableMergeArray(sources));
    }
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public static Completable mergeArray(CompletableSource... sources) {
        ObjectHelper.requireNonNull(sources, "sources is null");
        if (sources.length == 0) {
            return complete();
        } else
        if (sources.length == 1) {
            return wrap(sources[0]);
        }
        return RxJavaPlugins.onAssembly(new CompletableMergeArray(sources));
    }
Returns a Completable instance that subscribes to all sources at once and
completes only when all source Completables complete or one of them emits an error.
<p>
<img width="640" height="270" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Completable.mergeArray.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code mergeArray} does not operate by default on a particular {@link Scheduler}.</dd>
<dt><b>Error handling:</b></dt>
<dd>If any of the source {@code CompletableSource}s signal a {@code Throwable} via {@code onError}, the resulting
{@code Completable} terminates with that {@code Throwable} and all other source {@code CompletableSource}s are disposed.
If more than one {@code CompletableSource} signals an error, the resulting {@code Completable} may terminate with the
first one's error or, depending on the concurrency of the sources, may terminate with a
{@code CompositeException} containing two or more of the various error signals.
{@code Throwable}s that didn't make into the composite will be sent (individually) to the global error handler via
{@link RxJavaPlugins#onError(Throwable)} method as {@code UndeliverableException} errors. Similarly, {@code Throwable}s
signaled by source(s) after the returned {@code Completable} has been disposed or terminated with a
(composite) error will be sent to the same global error handler.
Use {@link #mergeArrayDelayError(CompletableSource...)} to merge sources and terminate only when all source {@code CompletableSource}s
have completed or failed with an error.
</dd>
</dl>
@param sources the iterable sequence of sources.
@return the new Completable instance
@throws NullPointerException if sources is null
@see #mergeArrayDelayError(CompletableSource...)