Re: general performance question

From:

Knute Johnson <nospam@rabbitbrush.frazmtn.com>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 30 Jan 2008 18:13:19 -0800

Message-ID:

<47a12eb8$0$27812$b9f67a60@news.newsdemon.com>

Mike Schilling wrote:

Matt Humphrey wrote:

"Tobi" <TobiMc3@gmail.com> wrote in message
news:628a2617-ff4a-460a-9c50-661e7f424f2f@s13g2000prd.googlegroups.com...

Is it *really* true that creating an object closer to where it will
be used by the code, rather than creating it and setting it to
null,
makes a noticeable difference performance-wise?

Clearly there's no sense at any time in creating an object and then
setting it to null, so I think you're mixing up variable declaration
with object creation.

There's this, which might not be what the OP had in mind:

    void method()
    {
        ...
        if (condition)
        {
            LargeObject lg = new LargeObject();
            lg.doStuff()
            // See discussion below
        }
        ...
    }

This has been discussed on this group, and the consensus is that the
method's stack frame continues to point to the LargeObject, so that it
can't be collected until the method returns. (It seems to me that the
JVM should be free to null out the reference once it goes out of
scope, or even if it's in scope but flow analysis makes it clear that
it can't be used any more, but that was a minority opinion.) Thus it
can make sense to replace the comment with

    lg = null;

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).

--

Knute Johnson
email s/nospam/knute/

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