A HashMap bug with a Proxy value?

Dmytro Sheyko dmytro_sheyko at hotmail.com
Thu Feb 17 09:21:19 UTC 2011

Hi Jing LV,

As for your patch of HashMap I think we shouldn't do this. There are a lot of places in code where we assume that every object equals to itself, not only in HashMap (e.g. ArrayList.indexOf()).
In you case I believe that InvocationHandler impl is broken because it written that way that violates contract of hashCode()/equals().


Date: Thu, 17 Feb 2011 16:24:23 +0800
From: lvjing at linux.vnet.ibm.com
To: core-libs-dev at openjdk.java.net
Subject: Re: A HashMap bug with a Proxy value?


    Hello, is there any other comments on this issue? Can someone help
    raise a bug on Sun's bug system? Thanks.



    于 2011-1-19 17:06, Jing LV 写道:
      Message body


             Thanks for information. I've raised a new bug on openjdk
      bug system (https://bugs.openjdk.java.net/show_bug.cgi?id=100165)
      with testcase and patch.


      于 2011-1-14 1:46, Jason Mehrens 写道:

        > I wonder the design for Proxy and InvocationHandler can be

        > enhanced by creating a default equals/toString/hashCode

        > for Proxy correctly, not ask developers to do it again and

        > 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


        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








Best Regards,
Jimmy, Jing LV 		 	   		  
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