src/main/java/io/reactivex/Flowable.java
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Single<List<T>> toSortedList() {
        return toSortedList(Functions.naturalComparator());
    }
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Single<List<T>> toSortedList() {
        return toSortedList(Functions.naturalComparator());
    }
Returns a Single that emits a list that contains the items emitted by the finite source Publisher, in a
sorted order. Each item emitted by the Publisher must implement {@link Comparable} with respect to all
other items in the sequence.

<p>If any item emitted by this Flowable does not implement {@link Comparable} with respect to
all other items emitted by this Flowable, no items will be emitted and the
sequence is terminated with a {@link ClassCastException}.
<p>
<img width="640" height="310" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/toSortedList.png" alt="">
<p>
Note that this operator requires the upstream to signal {@code onComplete} for the accumulated list to
be emitted. Sources that are infinite and never complete will never emit anything through this
operator and an infinite source may lead to a fatal {@code OutOfMemoryError}.
<dl>
<dt><b>Backpressure:</b></dt>
<dd>The operator honors backpressure from downstream and consumes the source {@code Publisher} in an
unbounded manner (i.e., without applying backpressure to it).</dd>
<dt><b>Scheduler:</b></dt>
<dd>{@code toSortedList} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
@return a Single that emits a list that contains the items emitted by the source Publisher in
sorted order
@see <a href="http://reactivex.io/documentation/operators/to.html">ReactiveX operators documentation: To</a>