It depends greatly on the problem domain. The difference might be near zero, or you might be able to get ~16x better performance (using say, AVX-512 intrinsics)

It depends greatly on the problem domain. The difference might be near zero, or you might be able to get ~16x better performance (using say, AVX-512 intrinsics). Then again, is intrinsics really C? Not really, but you can do it. What if you have to abandon using classes when you want to, in order to get the memory layout you want in Java, are you still using Java?