Hello. Reflection noob but I'm basically trying to...

# reflect

[Colton Idle]

Hello. Reflection noob but I'm basically trying to change the value of a static field in a java class.

Here's the java class: https://github.com/tink-crypto/tink-java/blob/main/src/main/java/com/google/crypto/tink/CryptoFormat.java

Here's my reflection code that fails:

val field = CryptoFormat::class.java.getDeclaredField("NON_RAW_PREFIX_SIZE")

     field.isAccessible = true
     
     val modifers = field.javaClass.getDeclaredField("modifiers")
     modifers.isAccessible = true
     modifers.setInt(field, field.modifiers and java.lang.reflect.Modifier.FINAL.inv())
     
     field.setInt(null, 2000)

     val newValue = CryptoFormat.NON_RAW_PREFIX_SIZE
     println("NON_RAW_PREFIX_SIZE is now: $newValue")

Error: java.lang.NoSuchFieldException: modifiers

[ephemient]

that's Java reflection, not Kotlin

[ephemient]

but basically Java has locked down reflective access to other modules since JPMS

[ephemient]

also even if you bypass that, it won't work

[ephemient]

Java compiler implicitly inlines static final values that follow certain rules (Kotlin makes it explicit with const), and this is one of them. so changing the value at runtime does nothing to existing code

[Colton Idle]

thanks for teaching!

[Klitos Kyriacou]

In any case, is this how you get field modifiers? That would work only if the field NON_RAW_PREFIX_SIZE was an instance of a class that had a field called modifiers. I think you meant to call getModifiers() instead.

[ephemient]

I think you're misreading the code. in older versions of Java, it was possible to bypass the final modifier in reflection by modifying (via reflection) the reflected Field. now you are not allowed to access java.base reflectively, so that trick no longer works