Is there an equivalent of Subject for RxJava's Single?

Question

In RxJava is there anything equivalent to the Subject class that works for a Single? Presumably I'd call its onSuccess( item ) or onError( Throwable ) methods and the output would be forwarded to the SingleSubscriber.

I guess I could use an Observable Subject and transform it to a Single but that seems a bit clunky.

Currently using RxJava 1 but interested in the situation with RxJava 2 also.

Answer 1

In RxJava 2 there is SingleSubject that you can use as follows:

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

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

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

subject1.onSuccess(1);

// onSuccess is a terminal event with SingleSubjects
// 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);

Unfortunately there is no equivalent available in RxJava 1. However, as you have mentioned, you can achieve the desired result by calling subject.toSingle().