I was listening to a podcast on SE Radio a few years ago when they were interviewing some high performance stock trader (or maybe even the NYSE engineers themselves, I don’t recall) and they were talking about how they used sun.misc.Unsafe to basically do the low level memory operations that lower level languages allow. I don’t remember their reasoning on why they were using Java instead of an actual low level language but it was still fascinating.

I think newer versions of the JDK have been making it difficult or impossible to access that class though.