Observable.never()

A close cousin of Observable.empty() is Observable.never(). The only difference between them is that it never calls onComplete(), forever leaving observers waiting for emissions but never actually giving any:

    import io.reactivex.Observable;

    public class Launcher {
      public static void main(String[] args) {

        Observable<String> empty = Observable.never();

        empty.subscribe(System.out::println,
          Throwable::printStackTrace,
            () -> System.out.println("Done!"));

        sleep(5000);

      }

      public static void sleep(int millis) {
        try {
          Thread.sleep(millis);
        } catch (InterruptedException e) {
          e.printStackTrace();
        }
       }
     } 

This Observable is primarily used for testing and not that often in production. We have to use sleep() here just like Observable.interval() because the main thread is not going to wait for it after kicking it off. In this case, we just use sleep() for five seconds to prove that no emissions are coming from it. Then, the application will quit.