src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.COMPUTATION)
    public final Observable<Observable<T>> window(long timespan, TimeUnit unit) {
        return window(timespan, unit, Schedulers.computation(), Long.MAX_VALUE, false);
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.COMPUTATION)
    public final Observable<Observable<T>> window(long timespan, TimeUnit unit) {
        return window(timespan, unit, Schedulers.computation(), Long.MAX_VALUE, false);
    }
Returns an Observable that emits windows of items it collects from the source ObservableSource. The resulting
ObservableSource emits connected, non-overlapping windows, each of a fixed duration specified by the
{@code timespan} argument. When the source ObservableSource completes or encounters an error, the resulting
ObservableSource emits the current window and propagates the notification from the source ObservableSource.
<p>
<img width="640" height="375" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/window5.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>This version of {@code window} operates by default on the {@code computation} {@link Scheduler}.</dd>
</dl>

@param timespan
the period of time each window collects items before it should be emitted and replaced with a
new window
@param unit
the unit of time that applies to the {@code timespan} argument
@return an Observable that emits connected, non-overlapping windows representing items emitted by the
source ObservableSource during fixed, consecutive durations
@see <a href="http://reactivex.io/documentation/operators/window.html">ReactiveX operators documentation: Window</a>