src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final Observable<T> subscribeOn(Scheduler scheduler) {
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
        return RxJavaPlugins.onAssembly(new ObservableSubscribeOn<T>(this, scheduler));
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.CUSTOM)
    public final Observable<T> subscribeOn(Scheduler scheduler) {
        ObjectHelper.requireNonNull(scheduler, "scheduler is null");
        return RxJavaPlugins.onAssembly(new ObservableSubscribeOn<T>(this, scheduler));
    }
@ CheckReturnValue @ SchedulerSupport ( SchedulerSupport . CUSTOM ) public final Observable < T > subscribeOn ( Scheduler scheduler ) { ObjectHelper . requireNonNull ( scheduler , "scheduler is null" ) ; return RxJavaPlugins . onAssembly ( new ObservableSubscribeOn < T > ( this , scheduler ) ) ; }
Asynchronously subscribes Observers to this ObservableSource on the specified {@link Scheduler}.
<p>
<img width="640" height="305" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/subscribeOn.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>You specify which {@link Scheduler} this operator will use.</dd>
</dl>

@param scheduler
the {@link Scheduler} to perform subscription actions on
@return the source ObservableSource modified so that its subscriptions happen on the
specified {@link Scheduler}
@see <a href="http://reactivex.io/documentation/operators/subscribeon.html">ReactiveX operators documentation: SubscribeOn</a>
@see <a href="http://www.grahamlea.com/2014/07/rxjava-threading-examples/">RxJava Threading Examples</a>
@see #observeOn
Asynchronously subscribes Observers to this ObservableSource on the specified { @link Scheduler } . <p > <img width = 640 height = 305 src = https : // raw . github . com / wiki / ReactiveX / RxJava / images / rx - operators / subscribeOn . png alt = > <dl > <dt > <b > Scheduler : < / b > < / dt > <dd > You specify which { @link Scheduler } this operator will use . < / dd > < / dl >