Efficiency of method call in for loop condition

Question

I am writing a game engine, in which a set of objects held in a ArrayList are iterated over using a for loop. Obviously, efficiency is rather important, and so

Answer 1

By specification, the idiom

for (String extension : assetLoader.getSupportedExtensions()) {
  ...
}

expands into

for (Iterator it = assetLoader.getSupportedExtensions().iterator(); it.hasNext();)
{
    String extension = it.next();
    ...
}

Therefore the call you ask about occurs only once, at loop init time. It is the iterator object whose methods are being called repeatedly.

However, if you are honestly interested about the performance of your application, then you should make sure you're focusing on the big wins and not small potatoes like this. It is almost impossible to make a getter call stand out as a bottleneck in any piece of code. This goes double for applications running on HotSpot, which will inline that getter call and turn it into a direct field access.