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From "Hope, Matthew" <Matthew.H...@capitalone.com>
Subject RE: Betwixt - CyclicReferenceException
Date Thu, 18 Sep 2003 16:15:06 GMT
A cyclical reference is when a loop exists in your object graph (or indeed
any type of graph)

If you have 
A- > B
B -> C
C -> A

Then a loop exists and if some algorithm is meant to 'walk' through the
graph and do something at each node (object) then in the situation above it
would walk forever going round in a loop.

Graph traversal (walk) algorithms often include mechanisms to avoid loops,
either by terminating in a failure state (throw an exception) or by not
traversing an edge to a node already visited.

This implementation is maintaining a set of nodes visited and when a node is
revisited it throws an exception.

One area where this can be a pain is if you have a structure

A -> B via variable x
A -> B via variable y

In this case a naïve algorithm will call this a revisit - I don't know if
betwixt does though

Your two examples would contain one which has no such loop and another which
does. Perhaps in one you are reusing an object in two different variables?

Matt

-----Original Message-----
From: Michael Watson [mailto:michael.watson@estafet.com] 
Sent: 18 September 2003 16:58
To: Jakarta Commons Users List
Subject: Betwixt - CyclicReferenceException


Hi,

I'm having issues with cyclic references and was wondering if anyone can
shed some light for me.

I'm calling BeanWriter.write (on a reasonably complex bean) and occasionally
getting a cyclicreferenceexception thrown.

I can reproduce the problem easily but the thing that's confusing me is that
I can call this method with another instance of the same type of bean (with
near identical data) and it doesn't throw an exception.

Can anyone explain exactly what a cyclic reference is, how I might be able
to identify what part of the bean is causing it and how I can try and avoid
it?

Thanks in advance.

Mike


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