How can I get accurately the execution time of a method?

Question

My first idea is:
long start =System.currentTimeMillis();
method call
long end =System.currentTimeMillis();
long executionTime= end-start;
I know this is a very trivial wat, I have not always the same accuracy with execution of the same method.
Do you have better idea to solve it?

Answer 1

Simple answer: you can't. Basically and in general because there always will be other threads running on your computer, be they java threads or other (native) threads.
But with java there is another problem as well. Your JVM might decide to compile your byte code into native code, thus giving different run time results.
What is generally done when someone needs an estimate of the runtime of some java method is to follow the following steps:
1) Run the method a considerable number of times to alert the JVM that it might benefit from compiling byte code to native code.
2) Give the JVM some rest by invoking sleep for some time. It may use that rest to do the compilation.
3) Run the method again a couple of times and calculate the average runtime.
This will give you some idea, when you have alternative implementations, what implementation is most efficient.
I'm fullly aware that this is not scientific, but it helps me sometimes,
Piet