This subject does not have a public constructor by design; a new non-terminated instance of this MaybeSubject can be created via the create() method.

Since the MaybeSubject is conceptionally derived from the Processor type in the Reactive Streams specification, nulls are not allowed (Rule 2.13) as parameters to onSuccess(Object) and onError(Throwable). Such calls will result in a NullPointerException being thrown and the subject's state is not changed.

Since a MaybeSubject is a io.reactivex.rxjava3.core.Maybe, calling onSuccess, onError or onComplete will move this MaybeSubject into its terminal state atomically.

All methods are thread safe. Calling onSuccess(Object) or onComplete() multiple times has no effect. Calling onError(Throwable) multiple times relays the Throwable to the io.reactivex.rxjava3.plugins.RxJavaPlugins#onError(Throwable) global error handler.

Even though MaybeSubject implements the MaybeObserver interface, calling onSubscribe is not required (Rule 2.12) if the subject is used as a standalone source. However, calling onSubscribe after the MaybeSubject reached its terminal state will result in the given Disposable being disposed immediately.

This MaybeSubject supports the standard state-peeking methods hasComplete(), hasThrowable(), getThrowable() and hasObservers() as well as means to read any success item in a non-blocking and thread-safe manner via hasValue() and getValue().

The MaybeSubject does not support clearing its cached onSuccess value.

Scheduler:

MaybeSubject does not operate by default on a particular io.reactivex.rxjava3.core.Scheduler and the MaybeObservers get notified on the thread where the terminating onSuccess, onError or onComplete methods were invoked.

Error handling:

When the onError(Throwable) is called, the MaybeSubject enters into a terminal state and emits the same Throwable instance to the last set of MaybeObservers. During this emission, if one or more MaybeObservers dispose their respective Disposables, the Throwable is delivered to the global error handler via io.reactivex.rxjava3.plugins.RxJavaPlugins#onError(Throwable) (multiple times if multiple MaybeObservers cancel at once). If there were no MaybeObservers subscribed to this MaybeSubject when the onError() was called, the global error handler is not invoked.

Example usage:

MaybeSubject<Integer> subject1 = MaybeSubject.create();

TestObserver<Integer> to1 = subject1.test();

// MaybeSubjects are empty by default
to1.assertEmpty();

subject1.onSuccess(1);

// onSuccess is a terminal event with MaybeSubjects
// TestObserver converts onSuccess into onNext + onComplete
to1.assertResult(1);

TestObserver<Integer> to2 = subject1.test();

// late Observers receive the terminal signal (onSuccess) too
to2.assertResult(1);

// -----------------------------------------------------

MaybeSubject<Integer> subject2 = MaybeSubject.create();

TestObserver<Integer> to3 = subject2.test();

subject2.onComplete();

// a completed MaybeSubject completes its MaybeObservers
to3.assertResult();

TestObserver<Integer> to4 = subject1.test();

// late Observers receive the terminal signal (onComplete) too
to4.assertResult();

History: 2.0.5 - experimental