RFR: 7057785 : (xs) Add note to hashCode() that support for self referential is optional

Mike Duigou mike.duigou at oracle.com
Wed Sep 4 18:44:47 UTC 2013

Hello all;

I have updated the proposed changeset for this issue. I have moved the note to the interface documentation for Collection and Map and made it more general:

> Some collection operations which perform recursive traversal of the
> collection may fail with an exception for self-referential instances where
> the collection directly or indirectly contains itself. This includes the
> {@code clone()}, {@code equals()}, {@code hashCode()} and {@code toString()}
> methods. Implementations may optionally handle the self-referential scenario,
> however most current implementations do not do so.

The webrev is at:



On Aug 27 2013, at 19:06 , Mike Duigou wrote:

> Hello all;
> Fairly frequently it is reported that various Collection/Map implementations of hashCode() fail when the instance directly or indirectly contains itself. For a variety of reasons, mostly performance and resource related, most implementations choose not to support calculation of hash codes for self-referential collections. This is not likely to change. So to reduce confusion and "bug" reports I am proposing a non-normative @apiNote be added to Collection and HashMap. The text of the proposed note is:
>> Support for calculation of hash code by self referential {Collection|Map}s (they either directly or indirectly contain themselves) is optional. Few Collection implementations support calculation of hash code for self referential instances.
> http://cr.openjdk.java.net/~mduigou/JDK-7057785/0/webrev/
> Cheers,
> Mike

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