A HashMap bug with a Proxy value?

Jason Mehrens jason_mehrens at hotmail.com
Thu Jan 13 17:46:35 UTC 2011

> I wonder the design for Proxy and InvocationHandler can be 
> enhanced by creating a default equals/toString/hashCode implementation 
> for Proxy correctly, not ask developers to do it again and again 
> whenever he uses Proxy. Anyway, this may be another story.

See: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4652876
The ProxyGenerator could safely add byte codes to equals/compareTo/compare that:
1. Handle the null case per contract: false, NPE, call handler.
2. Proxy == Argument: true, 0, 0
3. Proxy.getClass() == Argument.getClass() && Proxy.h == Proxy.getClass().cast(argument).h: true,0,0
The problem is short circuit operations nor return value overrides are not allowed per the Proxy contract: "A method invocation on a proxy instance through one of its proxy interfaces will be dispatched to the invoke method of the instance's invocation handler...the result that it returns will be returned as the result of the method invocation on the proxy instance."
I think for most equality checks, short circuit would be for the most part safe since most Collections all ready do such checks but, it requires a change to the Proxy contract which presents a compatibility problem.

> I think for HashMap, it may be benefit to check "==" as well as equals 
> in containsValue() (as containsKey already do) which is a quick solution 
> to resolve such problems.
Seems like the identity check would be a win: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6486197
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