Is there a limit to overriding final static field with Reflection?

Question

I have been faced in some of my Unit test with a strange behaviour with Reflection on final static field. Below is an example illustrating my issue.

I have a basic Singl

Answer 1

It's because of the JIT optimization. To prove this, disable it using the following VM option:

-Djava.compiler=NONE

In this case all 10_000 iterations will work.

Or, exclude the BasicHolder.getVALUE method from being compiled:

-XX:CompileCommand=exclude,src/main/BasicHolder.getVALUE

What actually happens under the hood is that after nth iteration, the hot method getVALUE is being compiled and static final Integer VALUE is being aggressively optimized (this is really the just-in-time constant¹). From this point, the assertion starts to fail.

The output of the -XX:+PrintCompilation with my comments:

val 1       # System.out.println("val " + BasicHolder.getInstance().getVALUE());
val 2
val 3
...
922  315    3    src.main.BasicHolder::getInstance (4 bytes)   # Method compiled
922  316    3    src.main.BasicHolder::getVALUE    (4 bytes)   # Method compiled
...
val 1563    # after compilation
val 1563
val 1563
val 1563
...

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^{1 - JVM Anatomy Park: Just-In-Time Constants.}