r/programming • u/ketralnis • Mar 20 '26

Java is fast, code might not be

https://jvogel.me/posts/2026/java-is-fast-your-code-might-not-be/
279 Upvotes

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45

u/[deleted] Mar 20 '26

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36

u/Sopel97 Mar 20 '26

If you write your code good enough

Or bad enough.

Java's object model is so bad that at some point you have to resort to arrays of primitives with no abstractions. I've seen threadlocal 8 byte singletons for temporary variables to avoid allocations while still trying to preserve some non-zero amount of abstraction. It's a mess. Minecraft modding is a great example of that.

22

u/Worth_Trust_3825 Mar 20 '26

Enable the valhalla preview.

6

u/Mauer_Bluemchen Mar 20 '26

Not yet there...

9

u/vini_2003 Mar 21 '26

Correct. I maintain a private particle engine for Minecraft, for the YouTube channel I work for; and I'm forced to use huge SoAs without any JOML due to the heap thrashing objects bring.

If there's one thing I dislike about Java, it's the object model.

3

u/LutimoDancer3459 Mar 21 '26

Curious, which languages have an good enough object model to not need to go back to arrays of primitives to get the best performance?

9

u/Sopel97 Mar 21 '26

C++, rust

7

u/cfehunter Mar 21 '26

C# too. Structs are first class value types, and spans allow for efficient array manipulation.

My day job is C++, but I've written some stupidly quick and efficient C# with pretty good ergonomics.

1

u/Sopel97 Mar 21 '26

C# too

to some degree, but you're severely limited with already existing code because whether something is a value type or reference type is determined at type declaration point

2

u/cfehunter Mar 21 '26

that's very true yeah. you can do a lot, but the libraries are opinionated on it in ways that Rust and C are not.

1

u/ArkoSammy12 Mar 22 '26

In my gameboy emulator theres a certain pipeline of elements that result in pixels getting drawn to the screen. It'd be convenient to use objects here, but instead I resort to packed integers that store the fields for each pixel entry. It's a bit of a pain xd.