Re: Need to protect method-local object against GC?

From:

Patricia Shanahan <pats@acm.org>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 09 Feb 2007 22:05:22 -0800

Message-ID:

<eqjnb3$5nf$1@ihnp4.ucsd.edu>

Steve Brecher wrote:

class Foo<Integer> implements Collection<Integer> {...}

class Bar {

    Foo<Integer> aFoo() {
        return new Foo<Integer>(...);
    }

    void method() {
        for (Integer i : aFoo())
            ...;
}

During the loop execution method will not have an instance of Foo on its
stack, but only an instance of Iterator<Integer>, and thus I think that
there is no instance of Foo that a garbage collector can see as live, and
hence the instance created by aFoo is subject to destruction during the
loop. Therefore it is necessary to write instead something like,

    myFoo = aFoo();
    for (Integer i : myFoo)
        ...;

Right?

I'm not sure about the distinction you are making. The second piece of
code is just a longer, more explicit, version one.

If the Iterator needs to reference some other object to do its job, it
is the responsibility of the Iterator implementation to ensure it either
has or can obtain that reference, not your worry when using the Iterator.

If the Iterator has or can obtain a reference to some Foo then as long
as the Iterator is reachable from some ongoing computation in an active
thread that Foo object is also reachable.

Patricia