Re: Ranking

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sun, 26 Aug 2007 15:33:17 -0400

Message-ID:

<RcydnXMQi57jSEzbnZ2dnUVZ_remnZ2d@comcast.com>

"Lew" wrote

ConcurrentModificationException is not inherently a threading issue. It
means something changed the underlying Collection but not through the
Iterator. Synchronization will not fix that.

Crouchez wrote:

Yep. I can confirm that Collection.synchronizedMap(map) with iterator throws
an concurrentmodificationexception with multithreading read/write. Hashtable
with enumeration [sic] works ok.

It'll throw that exception even without more than one thread.

So will Hashtable, if you use an Iterator.

When you said "enumeration", did you mean "Enumeration", as in
"java.util.Enumeration<E>"? If so then you are mistaken, it does not "work
ok" because there is no ability for the Enumeration to detect concurrent
modification. Therefore the code is silently breaking.

Again - ConcurrentModificationException is not inherently a threading issue.
It does not require more than one thread to happen. If you are getting that
exception, it's because you're not protecting the Map against "side" access,
ergo you're getting inconsistent or wrong results. The exception alerts you
to that issue. Using an Enumeration to hide the error doesn't mean the error
isn't happening.

--
Lew