Kotlin: Kotlin Activity cannot be extended. This type is final, so it cannot be inherited

Kotlin Programming

Question or issue of Kotlin Programming:

I have created a Kotlin Activity, but I am not able to extend the activity. I am getting this message: This type is final, so it cannot be inherited from. How to remove final from Kotlin’s activity, so it can be extended?

How to solve this issue?

Solution no. 1:

As per Kotlin documentation, 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.

open class Base {
    open fun v() {}
    fun nv() {}
}

class Derived() : Base() {
    override fun v() {}
}

Refer :https://kotlinlang.org/docs/reference/classes.html

Solution no. 2:

By default the Kotlin activity is final, so we cannot extend the class.
To overcome that we have to make the activity open so that, it can be extendable.

as like open class BaseCompatActivity : AppCompatActivity() { }

Solution no. 3:

In Kotlin, the classes are final by default that’s why classes are not extendable.


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.
Kotlin – Inheritance

open class Base(p: Int)

class Derived(p: Int) : Base(p)

Hope this helps!