How to use RxJava Interval Operator
<p>I'm learning about RxJava operator, and I found these code below did not print anything:</p>

<pre><code>public static void main(String[] args) {

    Observable
    .interval(1, TimeUnit.SECONDS)
    .subscribe(new Subscriber&lt;Long&gt;() {
        @Override
        public void onCompleted() {
            System.out.println("onCompleted");
        }

        @Override
        public void onError(Throwable e) {
            System.out.println("onError -&gt; " + e.getMessage());
        }

        @Override
        public void onNext(Long l) {
            System.out.println("onNext -&gt; " + l);
        }
    });
}
</code></pre>

<p>As ReactiveX, <code>interval</code></p>

<blockquote>
  <p>create an Observable that emits a sequence of integers spaced by a particular time interval</p>
</blockquote>

<p>Did I make a mistake or forget about something?</p>