src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <U> Observable<T> sample(ObservableSource<U> sampler) {
        ObjectHelper.requireNonNull(sampler, "sampler is null");
        return RxJavaPlugins.onAssembly(new ObservableSampleWithObservable<T>(this, sampler, false));
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <U> Observable<T> sample(ObservableSource<U> sampler) {
        ObjectHelper.requireNonNull(sampler, "sampler is null");
        return RxJavaPlugins.onAssembly(new ObservableSampleWithObservable<T>(this, sampler, false));
    }
@ CheckReturnValue @ SchedulerSupport ( SchedulerSupport . NONE ) public final < U > Observable < T > sample ( ObservableSource < U > sampler ) { ObjectHelper . requireNonNull ( sampler , "sampler is null" ) ; return RxJavaPlugins . onAssembly ( new ObservableSampleWithObservable < T > ( this , sampler , false ) ) ; }
Returns an Observable that, when the specified {@code sampler} ObservableSource emits an item or completes,
emits the most recently emitted item (if any) emitted by the source ObservableSource since the previous
emission from the {@code sampler} ObservableSource.
<p>
<img width="640" height="289" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/sample.o.nolast.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>This version of {@code sample} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param <U> the element type of the sampler ObservableSource
@param sampler
the ObservableSource to use for sampling the source ObservableSource
@return an Observable that emits the results of sampling the items emitted by this ObservableSource whenever
the {@code sampler} ObservableSource emits an item or completes
@see <a href="http://reactivex.io/documentation/operators/sample.html">ReactiveX operators documentation: Sample</a>
Returns an Observable that when the specified { @code sampler } ObservableSource emits an item or completes emits the most recently emitted item ( if any ) emitted by the source ObservableSource since the previous emission from the { @code sampler } ObservableSource . <p > <img width = 640 height = 289 src = https : // raw . github . com / wiki / ReactiveX / RxJava / images / rx - operators / sample . o . nolast . png alt = > <dl > <dt > <b > Scheduler : < / b > < / dt > <dd > This version of { @code sample } does not operate by default on a particular { @link Scheduler } . < / dd > < / dl >