Call extension function inside java class as any RX operator

Question

I created an extension function,

fun <T> Observable<T>.subscribeWithErrorHandling(onNext: (T) -> Unit ,onError: ((throwable: Throwable) -> Unit)? = null): Subscription {
//doing stuff
}

in kotlin class, I will be able to use it no problem in that way

observable.subscribeWithErrorHandling(...)

Now, I want to use this function in my java class as well. I already see that you can call it statically like :

MyExtensionFile.subscribeWithErrorHandling

But in my case, you need something else since it's a middle of an RX flow. And that is the part I'm stuck with. Does this is even possible? or no way to do something like that from the java code?

Answer 1

Simple answer. No.

Explanation - I believe that's not possible since that would mean you're extending the Observableclass which is abstract. Kotlin extensions add the same functionality by moving out of the inheritance tree and in Java in you're pretty much stuck with inheritance.

So the only option left would be to extend the base Observable class and create your own implementation of the same which I think would be unwanted in your case. A simple solution would be to create a new method just for Java which can take an observable and do the required logic. Or create a custom class with the Observable instance as its instance member and then write the required methods inside it (The standard OOPS way). This code could then be used from Kotlin as well as Java.

EDIT: I believe you already know this but will still point you to this question.

Answer 2

Extension functions one of the advantages of kotlin over Java. Coding in kotlin gives you those advantages, but unfortunately that does not mean you can have the kotlin language features in Java code.

Solution: port the module where you wish to use extension functions across to kotlin.