Re: general performance question

Knute Johnson <>
Thu, 31 Jan 2008 21:56:26 -0800
Mike Schilling wrote:

"Knute Johnson" <> wrote in message

Mike Schilling wrote:

"Knute Johnson" <> wrote in message

Mike Schilling wrote:

I don't think that is true. If you create an Object in a loop and
then reassign another Object to the same reference in the loop, the
first Object is eligible for garbage collection (and will be).

The previous poster didn't mention loops, merely a nested block
For a loop, the value set in the last iteration also leaks the


How can it if the reference is created in the block?

The method's stack frame isn't collected until the method exits; it has
no notion of block scope.

public void method() {
    Object oy = new Object();
    do {
        Object o = new Object();
    } while (false) ;

    // do other stuff

So I think we are talking about two different things here. o's objects
are created on the stack but go out of scope at the end of the do loop.

The "name" goes out of scope. The slot in the method stack frame that
corresponds to "o" is just another slot, exactly as if this had been

 public void method() {
     Object oy = new Object();
     Object o = new Object();

     // do other stuff

That is, block scopes within a method exist at compile-time, but not at

In your code snippet above, the objects that oy and o reference can be
GC'd when method() is exited. Are you saying that they can't? The same
would hold true for the references oy and o as well.

Yes, they can be collected when the method returns, but the object pointed
to by "o" in the first code snippet cannot be collected until the method
returns, even thouugh "o" is out of scope when the while loop completed.

But if you create a new object and reference it with o the old object
can be GC'd?

void method() {
     Object o = new Object();
     o = new Object();
     // the first object can be GC'd now before returning

I'm not sure where this would become an issue in a method without a
loop. Why would you create a large object in a method and use it for a
small percentage of the method's life in a really long live method?


Knute Johnson
email s/nospam/knute/

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