kotlin const val Const 'val' are only allowed on top level or in objects

Question

In my Kotlin project I want to declare constant on compile time:

So I use this:

@RunWith(AndroidJUnit4::class) class TradersActivityTest {      private lateinit var mockServer: MockWebServer     private const val ONE_TR = "no_wallets.json" // error here 

But I has compile time error:

Const 'val' are only allowed on top level or in objects 

How declare compile time constant?

Answer 1

const vals cannot be in a class. For you, this means you need to declare it top-level, in an object, or in a companion object (which also is exactly what the error message says).

Given it's private, a companion object one of the two options you can apply:

class TradersActivityTest {     ...     companion object {         private const val ONE_TR = "no_wallets.json"     } } 

Doing that makes it accessible to the class only.

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The second option is top-level. However, note that this exposes it to the rest of the file, not just the one class:

private const val ONE_TR = "no_wallets.json"  ...  class TradersActivityTest {     ... } 

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And just for the completeness of this answer, as I mentioned, the third option was an object:

object Constants {     const val ONE_TR = "no_wallets.json" } 

But it needs to be public to be accessed. Or alternatively internal, but it again depends on your target scope.