Kotlin Q2 is wrong

[westito]

https://github.com/Ebazhanov/linkedin-skill-assessments-quizzes/blob/main/kotlin/kotlin-quiz.md#q2-when-the-airplane-class-is-instantiated-it-displays-aircraft--null-not-aircraft--c130-why

Q2 is wrong. Abstract function can't be called (that's why it is abstract) so it can't return null. The answer closest to "A superclass is initialized before its subclass. Therefore, name has not been set before it is rendered", but this isn't really true either. If init{} in the Airplane class, then results will be the same.
The right answer is "init{} block runs before constructor". There is no reference linked and missing the instantiation line, C130 comes from nowhere.

[github-actions]

Hello @westito , thank you for submitting an issue! 👍 We highly appreciate it if you work on it as well.

[hientranea]

I also had the same issue with this question. The correct answer should be A superclass is initialized before its subclass. Therefore, name has not been set before it is rendered

Here is the long explanation:

abstract class Aircraft {
  init { println("Aircraft = ${getName()}") }
  abstract fun getName(): String
}
class Airplane(private val name: String) : Aircraft() {
  override fun getName(): String = name
}

When we create a new instance of Airplane, here are these steps which Kotlin does exactly underhood:

val obj = Airplane("C130")

1. Airplane's primary constructor is called. And it will trigger the primary constructor of the parent class first.
2. Airplan doesn't have an explicit primary constructor. Thus, the secondary constructor (init block) is called then.
3. In init block of Aircraft, the getName function of Airplane is called. And in this function, we access name field. This is the important key to the answer. The name field is only initialized until the primary constructor of Airplane is initialized completely. But we don't satisfy this condition at this time, so the null value returns instead.

By the way, if you pass the snippet code in IntelliJ IDEA, you will get the warning message from IDEA Calling non-final function getName in constructor. This is a common issue that is explained clearly in the Kotlin course made by JetBrains

[danielsacco]

Hi, despite this issue is closed I would also suggest to add this as reference for Q2.

[Ebazhanov]

Hi, despite this issue is closed I would also suggest to add this as reference for Q2.

Thanks for suggestion @westito, you can simply raise a PR with your suggestion/changes. Thank you in advance!

[danielsacco]

Done.
I didn't want to delete the reference to this interesting discussion, so I kept it as a "discussion" reference but it doesn't follow the same format as the rest of the questions.