Manage behaviour of an object at garbage collection??

Question

Hello.
I would like to specify that a counter is eventually decremented when an iterator is no longer in use. Is there some way to define the behaviour of an object when JRE realises that no references to it exist and proceeds to kill it?
I don't know very much about what Java does with data that is no longer used, so perhaps the notion is a preposterous one. Please advise.
Grape

Answer 1

I am also writing the collection thoroughly because I'll keep it in a general library
of data structures and patterns that I am building up
over time for reuse in the future.
Sounds cool but wouldn't it be easier to use one of the many container APIs that already exist and have been tested and are known to be reliable? That way you could concentrate on modeling the automata and not worry about measly collections. It doesn't sound very useful even as a learning experience since you must already be familiar with most kinds of containers. If you later find that you need a feature that's not in the standard collections, you can easily extend it or use an additional package like Collections from Jakarta Commons. http://jakarta.apache.org/commons/collections/
Should it be the iterator or the collection that calls the exception?You are the designer, it's your call.
Is there some kind of
ModificationListener that Iterator could implement,
so that when the collection is modified it sends out
something like a ModificationEvent that all Iterators
would get...? And the Iterators could then verify
that an exception should be thrown by checking
numModsAtStart != event.getSource().numMods()
But that would imply that the collection is aware of its iterators and also that iterators have to be both registered and de-registered with the collection. This approach has the same problems as the counting one you suggested before.
This use of the Observer pattern might be useful for other purposes.