Why is the Java ArrayList compatible with Kotlins List interface

Question

Why is this working

val foo: kotlin.collections.List<String> = java.util.ArrayList()

The ArrayList is not inheriting the Kotlin List, is it?

Answer 1

That's because kotlin.collections.List, among other types, is a mapped type: during compilation for the JVM, its usages are compiled into the corresponding usages of the Java java.util.List interface.