HashMap and visibility

Question

HashMap\'s javadoc states:

if the map is structurally modified at any time after the iterator is created, in any way except through the iterator\'s own re

Answer 1

If we will look into HashMap sources and compare them between Java 6 and Java 7 we will see such interesting difference:

transient volatile int modCount; in Java6 and just transient int modCount; in Java7.

I'm sure that it is cause for different behavior of mentioned code due to this:

        if (modCount != expectedModCount)
            throw new ConcurrentModificationException();

UPD: It seems to me, that this is a known Java 6/7 bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6625725 which was fixed in latest Java7.

UPD-2: Mr. @Renjith said, that he just tested and did not found any difference in behavior of HashMaps implementation. But I just tested it too.

My test was:

1) I have created HashMap2 class, which is absolutely copy of HashMap from Java 6.

One important thing is we need to introduce here 2 new fields:

transient volatile Set        keySet = null;

and

transient volatile Collection values = null;

2) Then I used this HashMap2 in test of this question and run it under Java 7

Result: it works like such test under Java 6, i.e. there isn't any ConcurentModificationException.

That all proves my conjecture. Q.E.D.