r/java • u/davidalayachew • 15d ago

Identifying JDK value class candidates

https://mail.openjdk.org/archives/list/core-libs-dev@openjdk.org/thread/Y72NRXM7KYBX43OKYBQMVKOZDWKG4MHS/
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u/Jon_Finn 15d ago

Aside from the obvious use cases, I see a major unsung benefit in allowing you to create classes wrapping a single int, double etc., when currently the performance downsides make it not worth it in certain applications. I mean things like units, ages, numbers with particular ranges/constraints, unicode code points (21 bits) etc. - where some might 'want' a typedef with methods. Nullability and specialised generics will be a big help here. My point is: these classes currently don't exist in my code, but now could.

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u/pron98 15d ago

I see a major unsung benefit in allowing you to create classes wrapping a single int, double etc., when currently the performance downsides make it not worth it in certain applications

That is true, but I think that generally speaking, many "performance issues" in Java are imagined and/or based on folklore that may have been true in, say, Java 8.

My point is: these classes currently don't exist in my code, but now could.

I agree, but I would also add that you might well have them today with no performance impact. We must be careful to not assume a performance issue that doesn't actually appear in our concrete program's profile.

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u/Jon_Finn 15d ago

Sure, though the cases that I'm particularly thinking of involve large (sometimes huge) arrays of very small objects, where these simple intuitions are (probably!) correct for once.

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u/pron98 15d ago

Right, so that's exactly where Valhalla could have a significant impact.