Re: Removing object from arraylist when pointed to by iterator

From:

"Mike Schilling" <mscottschilling@hotmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sun, 24 Aug 2008 10:32:09 -0700

Message-ID:

<sWgsk.19254$mh5.9263@nlpi067.nbdc.sbc.com>

Daniel Pitts wrote:

softwarepearls_com wrote:

On Aug 24, 3:00 am, "nooneinparticular314...@yahoo.com"
<nooneinparticular314...@yahoo.com> wrote:

I have an arraylist of objects of a certain type. I use an
iterator
on that arraylist to get the next instance of the object, using
the
iterator.next() method. But if I succeed in performing an
operation
on the object, I want to remove the object from my arraylist. The
question is how I remove it without calling .next() again, since
that will remove the next one, not the current one? ie. If I am
currently working on the object at position 4 in the arraylist
(through the iterator), I want to remove the object at position 4.
But I don't know what position the object is in because I got it
through the iterator.

I would say you're caught in the iterator "routine" so many fall
prey
to... you should not be using an iterator when working with an
ArrayList ! You should be iterating the "old fashioned" way ...
using
direct get(int) .. these don't entertain the concept of
ConcurrentModificationException. It's faster too.

Lies!

You don't see the concurrent modification errors, but they still can
cause bugs in your code!
Also, It isn't necessarily faster. I would assume its "about the
same" for the average program, but the benefits of using an iterator
far outweigh the cost for the average program. Fewer bugs, bugs
caught sooner, etc...

And it's easier to get right. Iterator.remove() does what the OP
wants. The equivalent with integer indices is:

for (int i = 0; i < list.length(); i++)
{
    if (shouldRemove(list.get(i))
    {
        list.remove(i);
        i--; // Needed to avoid skipping a list member.
                    // Or is it?
    }
}

And, when iterating the other way:

for (int i = list.length()-1; i >= 0; i--)
{
    if (shouldRemove(list.get(i))
    {
        list.remove(i);
        i++; // Needed to avoid skipping a list member.
                    // Or is it?
    }
}

The answers are "yes" and "no" respectively, but why take the chance
of getting it wrong?