Learning RxJava - Second Edition

Maybe

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

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

A given Maybe<T> emits 0 or 1 items. 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 a single item. Maybe.empty() creates a Maybe that emits nothing:

import io.reactivex.rxjava3.core.Maybe;public class Ch2_30a {    public static void main(String[] args) {        // has emission        Maybe<Integer> ...