True; Java makes it very easy to become memory-bound needlessly. No JIT in the world can save you if your primary data structure is a TreeMap<Long,Integer> with a billion entries.

C++ also makes it perfectly possible to build this kind of mess. I know because I've worked on the exact same situation you describe, except in that case the TreeMaps of pointers were hand-rolled, "tested in production", and yet another problem to maintain.(^)

Java might make it easier, and granted the extra object allocations around Longs and Integers will make it scale poorly more rapidly, but bad (or compromised) design and poor use of data structures is always going to lead to problems of some kind or another.

(^) Yes, I know about STL et al. Original programmer clearly did not.