src/main/java/io/reactivex/Flowable.java
@SuppressWarnings("unchecked")
    @CheckReturnValue
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Flowable<T> startWith(Iterable<? extends T> items) {
        return concatArray(fromIterable(items), this);
    }
@SuppressWarnings("unchecked")
    @CheckReturnValue
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Flowable<T> startWith(Iterable<? extends T> items) {
        return concatArray(fromIterable(items), this);
    }
Returns a Flowable that emits the items in a specified {@link Iterable} before it begins to emit items
emitted by the source Publisher.
<p>
<img width="640" height="315" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/startWith.png" alt="">
<dl>
<dt><b>Backpressure:</b></dt>
<dd>The operator honors backpressure from downstream. The source {@code Publisher}
is expected to honor backpressure as well. If it violates this rule, it <em>may</em> throw an
{@code IllegalStateException} when the source {@code Publisher} completes.</dd>
<dt><b>Scheduler:</b></dt>
<dd>{@code startWith} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param items
an Iterable that contains the items you want the modified Publisher to emit first
@return a Flowable that emits the items in the specified {@link Iterable} and then emits the items
emitted by the source Publisher
@see <a href="http://reactivex.io/documentation/operators/startwith.html">ReactiveX operators documentation: StartWith</a>