src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <R> Observable<R> flatMapMaybe(Function<? super T, ? extends MaybeSource<? extends R>> mapper) {
        return flatMapMaybe(mapper, false);
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <R> Observable<R> flatMapMaybe(Function<? super T, ? extends MaybeSource<? extends R>> mapper) {
        return flatMapMaybe(mapper, false);
    }
@ CheckReturnValue @ SchedulerSupport ( SchedulerSupport . NONE ) public final < R > Observable < R > flatMapMaybe ( Function < ? super T , ? extends MaybeSource < ? extends R > > mapper ) { return flatMapMaybe ( mapper , false ) ; }
Maps each element of the upstream Observable into MaybeSources, subscribes to all of them
and merges their onSuccess values, in no particular order, into a single Observable sequence.
<p>
<img width="640" height="310" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/flatMapMaybe.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code flatMapMaybe} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
@param <R> the result value type
@param mapper the function that received each source value and transforms them into MaybeSources.
@return the new Observable instance
Maps each element of the upstream Observable into MaybeSources subscribes to all of them and merges their onSuccess values in no particular order into a single Observable sequence . <p > <img width = 640 height = 310 src = https : // raw . github . com / wiki / ReactiveX / RxJava / images / rx - operators / flatMapMaybe . png alt = > <dl > <dt > <b > Scheduler : < / b > < / dt > <dd > {