Rxjava2 elementAt

elementAt的作用就是获取指定的数据

 Observable.just(1, 2, 3, 4, 5).elementAt(0).subscribe(new Consumer<Integer>() {
            @Override
            public void accept(Integer integer) throws Exception {
                System.out.println(integer);
            }
        });

 public final Maybe<T> elementAt(long index) {
        if (index < 0) {
            throw new IndexOutOfBoundsException("index >= 0 required but it was " + index);
        }
        return RxJavaPlugins.onAssembly(new ObservableElementAtMaybe<T>(this, index));
    }

调用到onNext时，当count与index一样时，数据流就可以结束了，并且将数据发射出来。

public void onNext(T t) {
            if (done) {
                return;
            }
            long c = count;
            if (c == index) {
                done = true;
                upstream.dispose();
                downstream.onSuccess(t);
                return;
            }
            count = c + 1;
        }