Difference between open and override methods in Kotlin?

Question

open class Base {

    open fun v() {}

    fun nv() {}
}

class Derived() : Base() {

    override fun v() {}
}

This is an example. Can someone please

Answer 1

The open annotation on a class is the opposite of Java's final: it allows others to inherit from this class as by default all classes in Kotlin are final. [Source]

Only after declaring a class as open we can inherit that class.

A method can only be overridden if it is open in the base class. Annotation override signals the overriding of base method by inheriting class.