title: How to use RxJava Interval Operator
body: <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>