Comment by winternewt

Maybe not slower once it has warmed up, though for memory-bandwidth bound use cases I would still say the lack of mutable records has you fighting the language to get reasonable cache locality (and everybody will hate your code for not being good Java). The fact that everything is a pointer kills the CPU execution pipeline and cache.

But even for I/O bound applications it still feels slow because excessive memory usage means more swap thrashing (slowing down your entire OS), and startup time suffers greatly from having to fire up VM + loading classes and waiting for the JIT to warm up.

I can start a C/C++/Rust based web server in under a second. The corresponding server in Java takes 10 seconds, or minutes once I have added more features.