CPU execution time in Java

Question

I want to calculate how much CPU time my function takes to execute in Java. Currently I am doing as below.

   long startTime = System.currentTimeMillis();
    myfunction();
    long endTime = System.currentTimeMillis();
    long searchTime = endTime - startTime;

But I found out that for the same I/P I get different time depending on system load.

So, how to get exact CPU time my function took to execute.

Answer 1

1. System.currentTimeMillis() will only ever measure wall-clock time, never CPU time.
2. If you need wall-clock time, then System.nanoTime() is often more precise (and never worse) than currentTimeMillis().
3. ThreadMXBean.getThreadCPUTime() can help you find out how much CPU time a given thread has used. Use ManagementFactory.getThreadMXBean() to get a ThreadMXBean and Thread.getId() to find the id of the thread you're interested in. Note that this method need not be supported on every JVM!