Question

I have been benchmarked my multihreaded program using -agentlib:hprof=cpu=samples
and was surprised to find the following line in the results:

rank   self  accum   count trace method
   1 52.88% 52.88%    8486 300050 java.lang.Object.hashCode

I never explicitly call hashCode() in my program.
What can be the reason for this? How can I understand the source for this time “waste” and whether it is normal or not?

Thanks,
David

Answer 1

Most likely you’re using very intensively a Map such as a HashMap.

HashMap used the hashCode to distribute the objects. If you’re using many objects with this data structure, is very important your .equals and your .hashCode method are properly implemented.

See: Effective Java Item 8: Always override hashCode when you override equals