How can I modify a `private val` inside a companion object through reflection?

# getting-started

[Lukasz Kalnik]

How can I modify a private val inside a companion object through reflection?

[Joffrey]

...but why?

[Lukasz Kalnik]

Because I inherited a very badly written legacy code base where Unit Tests are resorting to reflection to overwrite Android's LifecycleOwner.

[Lukasz Kalnik]

And I have to quickly fix the unit tests after a lifecycle library update. I cannot suddenly refactor the whole project.

[Lukasz Kalnik]

I read that it has to be done through Java Reflection:

val processLifecycleOwner = ProcessLifecycleOwner.get()
    val ownerInstance = processLifecycleOwner::class.java.getDeclaredField("newInstance")
    ownerInstance.isAccessible = true

    Field::class.java.getDeclaredField("modifiers").apply {
        isAccessible = true
        setInt(ownerInstance, ownerInstance.modifiers and Modifier.FINAL.inv())
    }

    ownerInstance.set(processLifecycleOwner, mockLifecycleOwner)

[Lukasz Kalnik]

However it gives me:

java.lang.NoSuchFieldException: modifiers

[ephemient]

you cannot do that on newer versions of the JVM

[Lukasz Kalnik]

Yes, I suppose that's the problem. Thanks!

[Lukasz Kalnik]

Anyway, it's a good opportunity to clean up the code instead of fixing the old hack 😉