Request for review: 7123229: (coll) EnumMap.containsValue(null) returns true

[Mike Duigou]

This looks correct. I appreciate the toString() method with a unique result. 

Mike

On Jan 9 2012, at 17:05 , Neil Richards wrote:

> Hi all,
> When proposing the change for 6312706 [1], I erroneously managed to
> convince myself (and others!) that it would be safe to use 'new
> Integer(0)' for java.util.EnumMap.NULL (the object used to mark null
> values for entries in the map) [2].
> 
> This was on the basis that I thought it was only compared by identity.
> However, on closer inspection, this turns out not to be the case.
> 
> 7123229 was raised to report the bug that was introduced based on this
> invalid assumption.
> 
> I've created a webrev with a suggested fix for 7123229 [3], which
> changes NULL to be an Object which:
>      * will only return 'true' from equals(Object) for itself
>      * returns 0 from hashCode()
> 
> For good measure, it also returns a sensible value from toString().
> 
> Please review this fix and let me know your thoughts,
> Thanks,
> Neil
> 
> [1] http://hg.openjdk.java.net/jdk7/tl/jdk/rev/c1e87a18e46a
> [2] http://mail.openjdk.java.net/pipermail/core-libs-dev/2011-March/006353.html
> [3] http://cr.openjdk.java.net/~ngmr/7123229/webrev.00/
> 
> -- 
> Unless stated above:
> IBM email: neil_richards at uk.ibm.com
> IBM United Kingdom Limited - Registered in England and Wales with number 741598.
> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
>