Comment by Calzifer

        for(int i=0;i<10000; ++i){

            // do nothing just compute hash again and again.
            hash = str.hashCode();
        }

"do nothing" is correct, "again and again" not so much. Java caches the hash code for Strings and since the JIT knows that (at least in recent version[1]) it might even remove this loop entirely.

[1] https://news.ycombinator.com/item?id=43854337