Learning RxJava

Maybe

Maybe is just like a Single except that it allows no emission to occur at all (hence Maybe). MaybeObserver is much like a standard Observer, but onNext() is called onSuccess() instead:

      public interface MaybeObserver<T> {      void onSubscribe(Disposable d);      void onSuccess(T value);      void onError(Throwable e);      void onComplete();    }

A given Maybe<T> will only emit 0 or  1 emissions. It will pass the possible emission to onSuccess(), and in either case, it will call onComplete() when done. Maybe.just() can be used to create a Maybe emitting the single item. Maybe.empty() will create a Maybe that yields no emission:

    import io.reactivex.Maybe;    public class Launcher {      public static void main(String[] args) {        // has emission        Maybe<Integer> presentSource ...