src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Observable<T> take(long count) {
        if (count < 0) {
            throw new IllegalArgumentException("count >= 0 required but it was " + count);
        }
        return RxJavaPlugins.onAssembly(new ObservableTake<T>(this, count));
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Observable<T> take(long count) {
        if (count < 0) {
            throw new IllegalArgumentException("count >= 0 required but it was " + count);
        }
        return RxJavaPlugins.onAssembly(new ObservableTake<T>(this, count));
    }
Returns an Observable that emits only the first {@code count} items emitted by the source ObservableSource. If the source emits fewer than
{@code count} items then all of its items are emitted.
<p>
<img width="640" height="305" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/take.png" alt="">
<p>
This method returns an ObservableSource that will invoke a subscribing {@link Observer}'s
{@link Observer#onNext onNext} function a maximum of {@code count} times before invoking
{@link Observer#onComplete onComplete}.
<dl>
<dt><b>Scheduler:</b></dt>
<dd>This version of {@code take} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param count
the maximum number of items to emit
@return an Observable that emits only the first {@code count} items emitted by the source ObservableSource, or
all of the items from the source ObservableSource if that ObservableSource emits fewer than {@code count} items
@see <a href="http://reactivex.io/documentation/operators/take.html">ReactiveX operators documentation: Take</a>