Why is “while (i++ < n) {}” significantly slower than “while (++i < n) {}”

Question

Apparently on my Windows 8 laptop with HotSpot JDK 1.7.0_45 (with all compiler/VM options set to default), the below loop

final int n = Integer.MAX_VALUE;
in         


        

Answer 1

I suggest you should (whenever possible) always use ++c rather than c++ as the former will never be slower since, conceptually, a deep copy of c has to be taken in the latter case in order to return the previous value.

Indeed many optimisers will optimise away an unnecessary deep copy but they can't easily do that if you're making use of the expression value. And you're doing just that in your case.

Many folk disagree though: they see it as as a micro-optimisation.