java compiler optimization

Question

Is the Java compiler smart enough to optimize loop below, by extracting the

Double average = new Double( totalTime / callCount ); 

out of t

Answer 1

This may seem like an obvious optimization at first, but I don't think so, since it involves object instantiation. Granted, it's an instantiation of an immutable primitive box type, but that still doesn't guarantee that there's no side effect.

I don't think any current compiler can optimize this. For this to be optimized, the compiler must be told that some classes have special properties (which can be a dangerous proposition given that things may change in the future). That is, the compiler must be told specifics of the API. This can not be optimized at the language-level alone.

If you use double, however, it's much more likely to be optimized (e.g. using the loop-invariant code motion technique).