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I think the risk is that the static robot reference is not guaranteed to be valid after a given round, so if you don’t update the reference things may not work as expected.

Yes, that's also what I guess, and since I'm updating the reference every round, I guess it would not be a problem. However, since robocode did not say what unwanted behavior it is, I'm worrying about more problems: race condition (since each round you have a new thread), GC problem (no longer a problem since robocode cleans static field each battle) and more

Since you're updating it every round, why do you need it to be static?

Ease of access, probably. I was doing the same before my big inversion of control refactoring.

because I’m simply making everything under a static variable, just like lazy singleton. The field itself is not static at all, but the field containing the field is static and has to be static. Diamond uses this style as well afak However the problem of static reference should happen to this style as well, since two approaches are fundamentally equivalent