Re: Vector (was Re: Change character in string)
On Fri, 13 Mar 2009 22:32:11 -0700, Lew <noone@lewscanon.com> wrote:
[...]
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof List))
return false;
ListIterator<E> e1 = listIterator();
ListIterator e2 = ((List) o).listIterator();
while(e1.hasNext() && e2.hasNext()) {
E o1 = e1.next();
Object o2 = e2.next();
if (!(o1==null ? o2==null : o1.equals(o2)))
return false;
}
return !(e1.hasNext() || e2.hasNext());
}
Interesting that they don't bother to check the size() first for equality,
but instead always enumerate at least all of the elements of the shorter
list.
[...]
I'm still not spotting the difference, exactly.
If I understand Bent's comments correctly:
Vector: for any given instance, the equals() method itself is
synchronized, and the getter to retrieve each element of the _other_
What getter? This is what I'm missing.
Sorry...Bent will have to provide the specifics, if you can't find the
details yourself. I haven't bothered to look at the source, nor even try
his example. I don't have enough interest myself to spend the time. I
assume you've confirmed it actually deadlocks as he says, so obviously
each thread is trying to take two different locks _somewhere_.
Since I have to guess, I'd guess that the list iterator is what winds up
calling a synchronized getter. Whether that's actually the get() method,
or some equivalent, I couldn't say (though, the get() method being the one
abstract method in AbstractList, it seems like a pretty good bet to me :)
).
Pete