Java Performance Tuning

Native Method Calls

For that extra zing in your application (but probably not applet), try out calls to native code. Wave goodbye to 100% pure Java certification, and say hello to added complexity to your development environment and deployment procedure. (If you are already in this situation for reasons other than performance tuning, there is little overhead to taking this route in your project.)

A couple of examples I’ve seen where native method calls were used for performance reasons were intensive number-crunching for a scientific application and parsing large amounts of data in restricted time. In these and other cases, the runtime application environment at the time could not get to the required speed using Java. I should note that the latter parsing problem would now be able to run fast enough in pure Java, but the original application was built with quite an early version of Java. In addition, some number crunchers find that the latest Java runtimes and optimizing compilers give them sufficient performance in Java without resorting to any native calls.^[23]

The JNI interface itself has its own overhead, which means that if a pure Java implementation comes close to the native call performance, the JNI overhead will probably cancel any performance advantages from the native call. However, on occasion the underlying system can provide an optimized native call that is not available from Java and cannot be implemented to work as fast in pure Java. In this kind of situation, ...