Java - Difference between for loop terminating expression

Question

I'm just curious: Is there a difference on speed and performance between this two loops implementation? Assume that size() method returns the length of the array,collection, or object that handles a group of elements (actually it's from XOM api).

Implementation 1:

int size = someArray.size();
for (int i = 0; i < size; i++) {
    // do stuff here
}

Implementation 2:

for (int i = 0; i < someArray.size(); i++) {
    // do stuff here
}

Answer 1

From a performance point of view, there is little difference. This is because a loop can be optimized so that the size() lookup is inlined, resulting in very little performance difference.

The main difference is if the size changes while looping. The first case will try to iterate a fixed number of times. In the second case, the number of iterations will depend on the final size().

Answer 2

The 1st snippet is bound to execute faster since it calls size() once only. The 2nd snippet calls size() N times. Depending on the impl. it might pose significant penalty, esp. if the compiler finds hard to inline the method and/or the size() method doesn't just return non-volatile variable, etc.

I'd have rewritten it like for(int i=0, s=someCollection.size(); i<s; i++)

Note: arrays don't have size() method.