But Kotlin doesn't have 100% interoperability! There are features in Kotlin which don't map nicely to Java features. For example you can't call methods with def

But Kotlin doesn't have 100% interoperability! There are features in Kotlin which don't map nicely to Java features. For example you can't call methods with default arguments from Java without resorting to unreadable hacks relying on a way defaults are implemented (same is true for Scala).