open class Base(p: Int)
class Derived(p: Int) : Base(p)
The open annotation on a class is the opposite of Java's final: it allows others to inherit from this class. By default, all classes in Kotlin are final, which corresponds to Effective Java, 3rd Edition, Item 19: Design and document for inheritance or else prohibit it.
The default visibility, used if there is no explicit modifier, is public.
