InterfaceInheritance.java

// In Java, I can do this
public class MainClass {
  interface MyInterface {
    public void printName();
  }
}

public class SubClass extends MainClass {
}

// Notice here that I use `SubClass.MyInterface` so the client doesn't know MainClass exists.
public void handleInterface(SubClass.MyInterface implementation) {
}

InterfaceInheritance.kt

// In Kotlin, I cannot do this
open class MainClass {
  interface MyInterface {
    fun printName()
  }
}

class SubClass : MainClass()

// This will not compile unless I do `MainClass.MyInterface`. See the Java notes about why I might want that.
fun handleInterface(implementation: SubClass.MyInterface) {
}