src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final ConnectableObservable<T> replay(final Scheduler scheduler) {
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
        return ObservableReplay.observeOn(replay(), scheduler);
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final ConnectableObservable<T> replay(final Scheduler scheduler) {
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
        return ObservableReplay.observeOn(replay(), scheduler);
    }
Returns a {@link ConnectableObservable} that shares a single subscription to the source ObservableSource that
will replay all of its items and notifications to any future {@link Observer} on the given
{@link Scheduler}. A Connectable ObservableSource resembles an ordinary ObservableSource, except that it does not
begin emitting items when it is subscribed to, but only when its {@code connect} method is called.
<p>
<img width="640" height="445" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/replay.o.s.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>You specify which {@link Scheduler} this operator will use.</dd>
</dl>

@param scheduler
the Scheduler on which the Observers will observe the emitted items
@return a {@link ConnectableObservable} that shares a single subscription to the source ObservableSource that
will replay all of its items and notifications to any future {@link Observer} on the given
{@link Scheduler}
@see <a href="http://reactivex.io/documentation/operators/replay.html">ReactiveX operators documentation: Replay</a>