I think what the GP is arguing is that if you want to be really fast you should forget using Java arrays and just wrap BLAS, LAPACK, etc., which are written in "close to the metal" languages, optimized within an inch of their life, have been around for decades, and are used by others with similar goals (numpy/scipy, etc.). As the GP says, Java libraries that already do this are probably available, so this may be a pretty trivial task.