src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final Observable<T> sample(long period, TimeUnit unit, Scheduler scheduler) {
        ObjectHelper.requireNonNull(unit, "unit is null");
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
        return RxJavaPlugins.onAssembly(new ObservableSampleTimed<T>(this, period, unit, scheduler, false));
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final Observable<T> sample(long period, TimeUnit unit, Scheduler scheduler) {
        ObjectHelper.requireNonNull(unit, "unit is null");
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
        return RxJavaPlugins.onAssembly(new ObservableSampleTimed<T>(this, period, unit, scheduler, false));
    }
@ CheckReturnValue @ SchedulerSupport ( SchedulerSupport . CUSTOM ) public final Observable < T > sample ( long period , TimeUnit unit , Scheduler scheduler ) { ObjectHelper . requireNonNull ( unit , "unit is null" ) ; ObjectHelper . requireNonNull ( scheduler , "scheduler is null" ) ; return RxJavaPlugins . onAssembly ( new ObservableSampleTimed < T > ( this , period , unit , scheduler , false ) ) ; }
Returns an Observable that emits the most recently emitted item (if any) emitted by the source ObservableSource
within periodic time intervals, where the intervals are defined on a particular Scheduler.
<p>
<img width="640" height="305" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/sample.s.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>You specify which {@link Scheduler} this operator will use.</dd>
</dl>

@param period
the sampling rate
@param unit
the {@link TimeUnit} in which {@code period} is defined
@param scheduler
the {@link Scheduler} to use when sampling
@return an Observable that emits the results of sampling the items emitted by the source ObservableSource at
the specified time interval
@see <a href="http://reactivex.io/documentation/operators/sample.html">ReactiveX operators documentation: Sample</a>
@see #throttleLast(long, TimeUnit, Scheduler)
Returns an Observable that emits the most recently emitted item ( if any ) emitted by the source ObservableSource within periodic time intervals where the intervals are defined on a particular Scheduler . <p > <img width = 640 height = 305 src = https : // raw . github . com / wiki / ReactiveX / RxJava / images / rx - operators / sample . s . png alt = > <dl > <dt > <b > Scheduler : < / b > < / dt > <dd > You specify which { @link Scheduler } this operator will use . < / dd > < / dl >