Re: Seeming Non-determinism in Java Programs

On Sunday 06 April 2008 17:56, Stephen Denne wrote:
> Randall R Schulz wrote:
> > ...
> >
> >
> > Has anyone else seen this sort of phenomenon? If so, how have
> > you dealt with it?
>
> I have encountered problems just like this.
> I can't recall the cause at the moment, I could probably figure it
> out based on my solution: I solved it by changing my usage of HashMap
> (or indirect use of HashMap within HashSet) to a LinkedHashMap. That
> way when iterating over the entries, the returned order is always the
> same. The order wasn't important to me, but variations in the order
> where observed, and variations resulted in different results from
> various heuristic algorithms.
>
> I think the reasons where due to Object.hashCode()
> Important bit from the Javadocs:
> (This is typically implemented by converting the internal address of
> the object into an integer, but this implementation technique is not
> required by the JavaTM programming language.)

But as far as I know (and certainly as I intended), no class whose
instances are stored in hashed structures rely on the default
implementation of hashCode(). That implementation is only congruent
with the default implementation of equals() as instance identity. I
never overload one of those without overloading the other, so this
should not be an explanation for what I'm seeing (thus leading to my
perplexity).


> The internal address varied between runs.
>
> Regards,
> Stephen Denne.


Randall Schulz

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