If I pass a method reference from Java to a Kotlin function, what do I put for parameter type? E.g.

MyJavaClass {
  MyKotlinClass myKotlinClass;

  void myMethod() { ... }

  ... myKotlinClass.foo(this::myMethod);
}

What should be the parameter in

fun foo( ? )

?

You can just use a normal Kotlin function, as they are a "functional interface" from Java's point of view. If you however need

void

as a return type, you need to use something like

Runnable

or

Consumer

from

java.util.function

or make your own functional interface.

My guess is it would be either

() -> Unit

or

() -> Nothing

() -> Unit

requires you to do

return kotlin.Unit.getINSTANCE()

(or something) from Java

It won’t be

() -> Nothing

. This type is a function/lambda that never returns normally (either it loops forever or it always throws an exception).

When I tried

() -> Unit

I had to do weird stuff in my Java function like

return Unit.INSTANCE