RFR : 7144488 StackOverflowError occurres on list via Collections.synchronizedList(List) (original) (raw)

David Holmes david.holmes at oracle.com
Thu Feb 23 21:31:49 UTC 2012

On 23/02/2012 10:41 PM, Doug Lea wrote:

On 02/22/12 21:44, David Holmes wrote:

I'm not a fan of collections containing themselves, but I think it is simple to fix contains(o)/contains[Key]|Value and remove(o) in a similar way. Though none of the wrapped collections currently handle that case, so I'm okay with not addressing this part.

It was a deliberate decision not to include any evasive schemes for collections that contain themselves, because the problem is unsolvable in general. The patch addresses those that directly contain themselves, but not the transitive closure, as in: c1 contains c2 that in turn contains c1. Our take was that it is a feature, not a bug, that anyone using equals or hashCode in such cases hits infinite recursion.

I must confess that I had misunderstood the basic issue here and thought that there was a problem independent of self-containment.

That said, an equals method that checks for o==this is pretty normal (and recommended by Effective Java Item 7) and we at least now have consistency amongst the wrapper classes. I'll add a note to the CR to that effect.

Michael: good to go (if it hasn't already)

Thanks, David

People are free to change policies about this, but do bear in mind that any changes along these lines are intrinsically incomplete.

(Although for pre-collections (Java1.1) legacy compatibility reasons, java.util.Hashtable.hashCode does include an ugly stopgap to avoid infinite recursion in the direct case.) -Doug

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