Agrona VS Eclipse Collections

Aeron for low latency apps and Agrona is you're using Aeron for data structures

Martin Thompson is one of the leaders in that space: his blog is a really great place to start. His Agrona library is a bunch of high-performance data structures, which you can use directly, but which can also serve as examples of writing such code.

ByteBuffer methods have quite a bit of overhead. You could further try to (1) writing to a byte[] first and then using the put(byte[]) method, or (2) use sun.misc.Unsafe::putByte (maybe try with Agrona's DirectBuffer and copy the necessary lines if need be).

eclipse-collections for Java.

Each year when I do the Advent of Code challenge I use it as an opportunity to learn a new language or tool chain. This year I am writing in Java 17 (I have not used Java since Java 8), along with Eclipse Collections, and using VS Code as my IDE.

If you want design like that, you can just use Eclipse Collections (https://www.eclipse.org/collections/). But do note that that design has its own problems if you are after perfection.

Eclipse-Collections

You were a little wrong, surely you can see that? And for Collections that don't autobox, you want to use something like https://github.com/eclipse/eclipse-collections