As a corollary, many Java programs rely really heavily on very thick layers of abstraction (in my day-to-day on a multi-node "enterprise" Java app I regularly s

As a corollary, many Java programs rely really heavily on very thick layers of abstraction (in my day-to-day on a multi-node "enterprise" Java app I regularly see stack traces of 200-500 function calls), and it's important to keep each slice of those abstractions as thin as possible. As another reply pointed out, much better to do some hinky things with the JVM then to call out through the native interface every time you need high performance for a tight loop.