src/main/java/io/reactivex/Single.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Future<T> toFuture() {
        return subscribeWith(new FutureSingleObserver<T>());
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Future<T> toFuture() {
        return subscribeWith(new FutureSingleObserver<T>());
    }
Returns a {@link Future} representing the single value emitted by this {@code Single}.
<p>
<img width="640" height="467" src="https://github.com/ReactiveX/RxJava/wiki/images/rx-operators/Single.toFuture.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code toFuture} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@return a {@link Future} that expects a single item to be emitted by this {@code Single}
@see <a href="http://reactivex.io/documentation/operators/to.html">ReactiveX documentation: To</a>