A profiler provides the developer (or performance specialist) with detailed information concerning, among other things, where a Java program is spending most of its time. It is a truism that most programs spend 80% of their execution time in 20% of the code. One of the most useful features of a profiler is to (inobtrusively) enable you to find out which methods in your code are 'slow' and which methods would, through optimisation, yield the biggest performance improvement.

Java comes with a built in profiler, but the advantage of applications like jProbe and OptimizeIt! is that they offer richer functionality such as visual method trace, support for threads, enforced garbage collection, etc.

All told a profiler is a very useful piece of kit when seeking to improve the performance of your application...

Hope this helps,

Dermot