src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Observable<T> concatWith(ObservableSource<? extends T> other) {
        ObjectHelper.requireNonNull(other, "other is null");
        return concat(this, other);
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Observable<T> concatWith(ObservableSource<? extends T> other) {
        ObjectHelper.requireNonNull(other, "other is null");
        return concat(this, other);
    }
@ CheckReturnValue @ SchedulerSupport ( SchedulerSupport . NONE ) public final Observable < T > concatWith ( ObservableSource < ? extends T > other ) { ObjectHelper . requireNonNull ( other , "other is null" ) ; return concat ( this , other ) ; }
Returns an Observable that emits the items emitted from the current ObservableSource, then the next, one after
the other, without interleaving them.
<p>
<img width="640" height="380" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/concat.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code concatWith} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param other
an ObservableSource to be concatenated after the current
@return an Observable that emits items emitted by the two source ObservableSources, one after the other,
without interleaving them
@see <a href="http://reactivex.io/documentation/operators/concat.html">ReactiveX operators documentation: Concat</a>
Returns an Observable that emits the items emitted from the current ObservableSource then the next one after the other without interleaving them . <p > <img width = 640 height = 380 src = https : // raw . github . com / wiki / ReactiveX / RxJava / images / rx - operators / concat . png alt = > <dl > <dt > <b > Scheduler : < / b > < / dt > <dd > { @code concatWith } does not operate by default on a particular { @link Scheduler } . < / dd > < / dl >