What can I pass to a Java method that expects a `Void!`?

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[Ellen Spertus]

What can I pass to a Java method that expects a Void!?

[Ellen Spertus]

The Java class is parameterized.

[Pablichjenkov]

Did you try null is the only thing that comes to my mind.

[Ellen Spertus]

@Pablichjenkov Thank you! That works. I didn't think of that because of the !.

[pt]

If memory serves, there is no instance of a Nothing type, null is the only value of a Nothing? type

[Pablichjenkov]

Exactly, I missed the nullable mark

[streetsofboston]

A void/Void in Java is Unit in Kotlin and has only one value Unit.
Passing a null (Unit?) may indeed work as well.

The type Nothing has no values at all (which means you can't create one, get one or pass one). The type Nothing? has only one value (null) and is a sub-type of all other types T? (including Unit?).

[karelpeeters]

Java's Void is more like Kotlin Nothing? than Unit.

[streetsofboston]

All Java methods returning the primitive void return Unit in Kotlin. Void is a nullable version of void in Java (much like int vs Integer), which would be Unit? in Kotlin.

[karelpeeters]

Well primitive void is nothing like the class Void.

[streetsofboston]

You're right about how Void is designed, with a private constructor and no public singleton or factory methods returning one, much like the design of Nothing.

[Pablichjenkov]

In plain English, I would relate Void with Emptyness or Nothing. Don't know if the language designers pursued this semantic.
Now as Anton said the fact of java methods returning void needing to return Unit in kotlin makes one to think that they are equivalent.
To me this void -> Unit transformation is basically a trick to bridge an imperative paradigm with a functional paradigm. But when it comes to the typing system itself I am more into Void being more Nothing than Unit.

[karelpeeters]

void is not like Nothing at all, void simply means a function doesn't return anything but Nothing means it never returns!