Emitter vs. Observer - what is the difference?

[dkhmelenko]

I discovered that there are two interfaces Emitter and Observer. Both of them have similar methods. The question is where should each of them be used?
Because Observable.create() receives as a parameter type Emitter and PublishSubject.subscribe() receives as a parameter type Observer (or Consumer). What makes impossible to use Emitter for subscribing in subject (and that was possible in RxJava 1.x).

Can somebody clarify or update documentation what is the difference between all of them and when should they be used?

[akarnokd]

The Emitter is an abstraction over Observer that handles cancellation for you. In 1.x it extends Observer because that interface is just 3 methods. In 2.x the Observer has a 4th method, onSubscribe which you should not interact with but can't hide it if 2.x Emitter extended Observer. The sole purpose of Emitter is to let you interact with the downstream in a safe manner from within Observable.create.

[dkhmelenko]

@akarnokd Thanks for explanation.
Because before I used Observer from Observable.create() to subscribe it to PublishSubject.subscribe(). But what is the best practice now as I cannot use Emitter for subscibing in Subject?

I would appreciate if you share some good approach of dealing with Observable.create() and Subject.subscibe().

[akarnokd]

Depends on what you were trying to do and why the indirection? Chain calls on PublishSubject directly for example, wrap the Emitter into an Observer.

[dkhmelenko]

@akarnokd Thanks for you suggestions. I'll give you my example, just in case and better understanding the issue.
I just wanted to wrap some async functions (like location request) with callbacks into Rx way. So I do function call in Observable.create(), but in order to handle the results of that async function from listener, I subscribe subsciber to subject and then that subject emits a value when callback is called.

[dkhmelenko]

Anyway, for my purposes I will go with your suggestion wrapping Emitter into an Observer.
Thank you. This question is answered.

[akarnokd]

Great!