src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <U> Observable<T> debounce(Function<? super T, ? extends ObservableSource<U>> debounceSelector) {
        ObjectHelper.requireNonNull(debounceSelector, "debounceSelector is null");
        return RxJavaPlugins.onAssembly(new ObservableDebounce<T, U>(this, debounceSelector));
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <U> Observable<T> debounce(Function<? super T, ? extends ObservableSource<U>> debounceSelector) {
        ObjectHelper.requireNonNull(debounceSelector, "debounceSelector is null");
        return RxJavaPlugins.onAssembly(new ObservableDebounce<T, U>(this, debounceSelector));
    }
Returns an Observable that mirrors the source ObservableSource, except that it drops items emitted by the
source ObservableSource that are followed by another item within a computed debounce duration.
<p>
<img width="640" height="425" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/debounce.f.png" alt="">
<p>
The delivery of the item happens on the thread of the first {@code onNext} or {@code onComplete}
signal of the generated {@code ObservableSource} sequence,
which if takes too long, a newer item may arrive from the upstream, causing the
generated sequence to get disposed, which may also interrupt any downstream blocking operation
(yielding an {@code InterruptedException}). It is recommended processing items
that may take long time to be moved to another thread via {@link #observeOn} applied after
{@code debounce} itself.
<dl>
<dt><b>Scheduler:</b></dt>
<dd>This version of {@code debounce} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param <U>
the debounce value type (ignored)
@param debounceSelector
function to retrieve a sequence that indicates the throttle duration for each item
@return an Observable that omits items emitted by the source ObservableSource that are followed by another item
within a computed debounce duration
@see <a href="http://reactivex.io/documentation/operators/debounce.html">ReactiveX operators documentation: Debounce</a>