kotlin 中的静态最终字段继承

Question

I have a really simple question here, but can't figure it out. Consider a java class:

class A {
    public static final int AA=5;
}

which translates (internally) into kotlin as this:

open class A {
    companion object {
        val AA:Int=5
    }
}

At least that's what I assume. Now if you inherit in java:

class B extends A {
    int AAA;
}

you can access field AA (from A) through B like this: B.AA . However, in Kotlin it's impossible. The only way to access it is through A.AA. Is this a built-in feature or I am doing something wrong?

Answer 1

In Java, when the compiler sees B.AA , it automatically transforms it into A.AA . There's no real inheritance or overriding there.

Kotlin's developers decided not to emulate this feature, because it doesn't fit with thinking of static methods as belonging to an object : the companion object of B doesn't extend the companion object of A , and can't because you can't extend an object .

Note that similarly, in Java you can access the field via a.AA where a is an instance of A ; you can't do that in Kotlin either.