Extremely easy to fix. Turn it into a record. I’m also pretty sure that cracking final fields is already disabled by default.

> Extremely easy to fix.

Nope, if the deserializer is initializing that field by directly setting values both by the field and by the internals of the field, it'll be a problem. The fix is to update the deserializer to a newer version. Apache Fury recently fixed this very issue, but it still relies on internal JDK APIs in order to do it's work.

> I’m also pretty sure that cracking final fields is already disabled by default.

Nope. There's sun.misc.Unsafe apis that allow for cracking and modifying those final fields. There are new jdk.internal APIs for doing the same that you'd have to move over to in order to accomplish the same. This JEP is about making final (mostly) meaning final. At very least, it will enforce that final once observed is final with the internal APIs allowing a final field to be set once, just outside the constructor.