Difference between declaring variables before or in loop?

Question

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 (q

Answer 1

I've always thought that if you declare your variables inside of your loop then you're wasting memory. If you have something like this:

for(;;) {
  Object o = new Object();
}

Then not only does the object need to be created for each iteration, but there needs to be a new reference allocated for each object. It seems that if the garbage collector is slow then you'll have a bunch of dangling references that need to be cleaned up.

However, if you have this:

Object o;
for(;;) {
  o = new Object();
}

Then you're only creating a single reference and assigning a new object to it each time. Sure, it might take a bit longer for it to go out of scope, but then there's only one dangling reference to deal with.