Difference between declaring variables before or in loop?

by

I have always wondered if, in general, declaring a throw-away variable before a loop, as opposed to repeatedly inside the loop, makes any (performance) difference?
A (quite pointless) example in Java:

a) declaration before loop:

double intermediateResult;
for(int i=0; i < 1000; i++){
    intermediateResult = i;
    System.out.println(intermediateResult);
}

b) declaration (repeatedly) inside loop:

for(int i=0; i < 1000; i++){
    double intermediateResult = i;
    System.out.println(intermediateResult);
}

Which one is better, a or b?

I suspect that repeated variable declaration (example b) creates more overhead in theory, but that compilers are smart enough so that it doesn’t matter. Example b has the advantage of being more compact and limiting the scope of the variable to where it is used. Still, I tend to code according example a.

Edit: I am especially interested in the Java case.

26 Answers
26

Leave a Comment