profilers for programming languages

I am working on Profilers. Can anyone list out the a开发者_JS百科dvantages of using profilers.

How Java profilers work? What technologies to use? Please if you have some good articles then forward me the links.

Thanx.

I have used both JProfiler and YourKit. The advantage of using a profiler is that you can find what parts of your code really cost time by measuring, rather than theorizing.

Both work by using a JVM agent and JVMTI (the Java Virtual Machine Tool Interface): http://download.oracle.com/javase/6/docs/platform/jvmti/jvmti.html