good place to declare variable

[Hendra Kurniawan]

Which one is better?

for(int i=0;i<Integer.MAX_VALUE;i++){

  MyObject o=new MyObject();

}

or

MyObject o=null;
int i;

for(i=0;i<Integer.MAX_VALUE;i++){

  o=new MyObject();

}

which is better for performance, which is better for memory? or even better, which is better for both? or no difference at all?

[Jeff Verdegan]

It makes no difference at all. All of a method's local variables are allocated at once, on method entry.

Good programming style dictates that we declare the variable in the smallest scope in which it is used, and also that we don't initialize to a value at declaration unless that value is actually meaningful and expected to be used in our method.

So in your case, even if you declared outside the loop, you'd skip the = null part, since there's no meaning or reason for it. However, since you're only using the variable inside the loop, you should declare it inside the loop anyway, so that becomes a moot point.

[Deepak Bala]

What Jeff said

which is better for performance ?

Neither

which is better for memory?

Neither. Since you create objects anyway.

no difference at all?

Yes, no difference whatsoever.

[Chris Hurst]

Seems the first one is better which is probably what most people would guess ;-)

Why the second doesn't have to null a local but I guess that was obvious ;-) a class member it would have had to.

- Would this give you a measurable improvement .. nope

I only did this for personal interest, I used a class viewer on similar code in Java 6 and one appears to have to null the variable and took two more lines of byte code, will the JIT just drop the difference ? / any impact on escape analysis ? Do we care ? ;-)

[Winston Gutkowski]

Hendra Kurniawan wrote:Which one is better?

The fact is, they're both crap.

Why? Because they simply create 2 billion objects for no apparent reason.

For any question like this to have any meaning, it's got to have some context; otherwise...read the words of Wulf (below).

Winston