title: How to make RxJava interval to perform action instantly
body: <p>Hello I am making observable to ask my server about its online/offline status every 15 seconds:</p>
  
  <pre><code>public Observable&lt;Response&gt; repeatCheckServerStatus(int intervalSec, final String path) {
          return Observable.interval(intervalSec, TimeUnit.SECONDS)
                  .flatMap(new Func1&lt;Long, Observable&lt;Response&gt;&gt;() {
                      @Override
                      public Observable&lt;Response&gt; call(Long aLong) {
                          return Observable.create(new Observable.OnSubscribe&lt;Response&gt;() {
                              @Override
                              public void call(Subscriber&lt;? super Response&gt; subscriber) {
                                  try {
                                      Response response = client.newCall(new Request.Builder()
                                              .url(path + API_ACTION_CHECK_ONLINE_STATUS)
                                              .header("Content-Type", "application/x-www-form-urlencoded")
                                              .get()
                                              .build()).execute();
  
                                      subscriber.onNext(response);
                                      subscriber.onCompleted();
                                      if (!response.isSuccessful())
                                          subscriber.onError(new Exception());
                                  } catch (Exception e) {
                                      subscriber.onError(e);
                                  }
                              }
                          })
                                  .subscribeOn(Schedulers.io())
                                  .observeOn(AndroidSchedulers.mainThread());
                      }
                  });
  
      }
  </code></pre>
  
  <p>After I call this method, first execution of code will be after intervalSec time (15sec in my case). Looking at rxJava docummentation of interval method:</p>
  
  <p><a href="http://reactivex.io/documentation/operators/interval.html" rel="noreferrer">http://reactivex.io/documentation/operators/interval.html</a></p>
  
  <p>This is how it should be. </p>
  
  <p>Question: is there any way to execute code instantly and then repeat in intervals?</p>