Others have mentioned IntMap, and in a more general way, I'd recommend treating those standard classes as a general-purpose implementation that should be replac

Others have mentioned IntMap, and in a more general way, I'd recommend treating those standard classes as a general-purpose implementation that should be replaced be specialized implementations -- to improve performance, memory footprint etc. -- WHERE NEEDED (avoid premature optimization!), and forget about it in the remaining 99% of cases where a HashMap contains less than 100 entries. It's true that C/C++/Rust don't have this problem because they are optimized for this. OTOH if the problem you are solving is more suitable to garbage collection than manual or static-analysis based memory management then Java's high-performance GC will shine.