I am implementing Page Object Model for mobile application automation framework. For readability for each page I want to have 2 classes – Page itself having properties and basic functions only and Steps to have all other methods.
I want to create abstract class with some abstract methods and then force all classes that inherit from this class to have implementation only for these needed overridden methods, no more.

I tried to create classes as follows:

abstract class A() {
    abstract fun foo()
    abstract fun bar()
}

final class ImplA(): A() {
    override fun foo() { println("foo") }
    override fun bar() { println("bar") }
    fun baz() { println("baz") } //not wanted
}

Then creating all object of class ImplA() casted directly to abstract class A():

fun main() {
    val tmp = ImplA() as A()
    tmp.foo()
    tmp.bar()
    tmp.baz()
}

In such case I got exception when calling tmp.baz(). I see 2 problems with this solution:

1. I need to remember to cast every object to abstract class.
2. Nothing prevents defining other (non overridden) methods in classes.

Is there any other way of preventing defining non overridden methods in classes?