The runtime system seems to be fine with this, at least the results for scala code (which compiles to bytecode consisting of many small, mostly immutable classe

The runtime system seems to be fine with this, at least the results for scala code (which compiles to bytecode consisting of many small, mostly immutable classes with shot lived instances) indicate that this style of programming hits a sweet spot for the JIT compiler and the GC (at least for sun's server VM) which has a far easier time inlining things than with code consisting of few big classes with long lived objects.