Saturday, 4 May 2019
java - Difference between declaring variables before or in loop?
Answer
Answer
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.
Answer
Which is better, a or b?
From a performance perspective, you'd have to measure it. (And in my opinion, if you can measure a difference, the compiler isn't very good).
From a maintenance perspective, b is better. Declare and initialize variables in the same place, in the narrowest scope possible. Don't leave a gaping hole between the declaration and the initialization, and don't pollute namespaces you don't need to.
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