Observable.future()

RxJava Observables are much more robust and expressive than Futures, but if you have existing libraries that yield Futures, you can easily turn them into Observables via Observable.future():

    import io.reactivex.Observable;
    import java.util.concurrent.Future;

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

        Future<String> futureValue = ...;
        
        Observable.fromFuture(futureValue)
          .map(String::length)
          .subscribe(System.out::println);
      }
    }