Kotlin: Interface … does not have constructors

15    3 months ago

I am converting some of my Java code to Kotlin and I do not quite understand how to instantiate interfaces that are defined in Kotlin code. As an example, I have an interface (defined in Java code):

public interface MyInterface {
    void onLocationMeasured(Location location);

And then further in my Kotlin code I instantiate this interface:

val myObj = new MyInterface { Log.d("...", "...") }

and it works fine. However, when I convert MyInterface to Kotlin:

interface MyInterface {
    fun onLocationMeasured(location: Location)

I get an error message: Interface MyListener does not have constructors when I try to instantiate it - though it seems to me that nothing has changed except syntax. Do I misunderstand how interfaces work in Kotlin?

Answers { 1 }
3 months ago

Your Java code relies on SAM conversion - an automatic conversion of a lambda into an interface with a single abstract method. SAM conversion is currently not supported for interfaces defined in Kotlin. Instead, you need to define an anonymous object implementing the interface:

val obj = object : MyInterface {
    override fun onLocationMeasured(location: Location) { ... }