How can an application be rewritten in machine code and interfaced with Java?

Question

I was reading The Java Language Environment. In the High Performance section I found this block

Applications requiring large amounts of compute power can be designed such that compute-intensive sections can be rewritten in native machine code as required and interfaced with the Java platform.

I didn't get it in fact, so how can an application be written in native machine code and interfaced with the Java platform?

Answer 1

You can use JNI to interface with native code.

Answer 2

Be sure this is really what you want/need. Modern JVM offers a lot of performances in terms of Java code optimization, so "simple" Java is often enough.

JNI is powerful, but it brings a lot of headaches ...