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From: Dovlecel Alexandru Ovidiu <alexandru.dovlecel@siemens.com>
To: "'Apache Torque Users List'" <torque-user@db.apache.org>
Subject: RE: hashCode/equals contract broken in BaseObject
Date: Tue, 4 May 2004 17:28:09 +0300 
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I think the approach that you provide will not work, because the XOR
operation will produce overlapping hashkeys. For example the following two
couples will provide the same key, even though they are different objects:

(class.hashCode in binary, pk.hashCode in binary) --> object.hashCode

(1110, 0001)  --> 1111
(1010, 0101)  --> 1111

So an object of type identified by 1110 (14) that has the pk.hashCOde equal
to 1
WILL BE EQUAL 
with an object of type identified by 1010 (10) that has the pk.hashcode
equal to 5

If I am wrong (I am not too good with the binary operations and the binary
format) pls correct me... 

Enjoy,
Alex 




-----Original Message-----
From: Shevek [mailto:shevek@anarres.org]
Sent: Tuesday, May 04, 2004 4:22 PM
To: Apache Torque Users List
Subject: RE: hashCode/equals contract broken in BaseObject


On Tue, 4 May 2004, Dovlecel Alexandru Ovidiu wrote:

> You can use torque objects as hash keys with one condition: 
> 
> all the keys in the hashtable must be instances of the same torque class.
> Then you will not have any inconsistency. 

I know this. However, this is in violation of the equals() contract and
causes much breakage. equals() should return true if and only if the
objects are equal. I have a requirement to mix class types. I have
suggested a fix for this: use

	getClass().hashCode() ^ key.hashCode()

instead of

	key.hashCode()

Then the whole world will work as intended again.

S.

> -----Original Message-----
> From: Shevek [mailto:shevek@anarres.org]
> Sent: Tuesday, May 04, 2004 4:07 PM
> To: Apache Torque Users List
> Subject: hashCode/equals contract broken in BaseObject
> 
> 
> hashCode and equals in BaseObject rely only on the primary key. This
> breaks horribly (violates the general contract of hashCode()/equals()) if 
> you compare two objects of different classes.
> 
> It MUST compare ob.getClass() as well as ob.getPrimaryKey() and include
> ob.getClass().hashCode() in its hashCode() [by xor?] [or something
> equivalent].
> 
> No doubt the reason for this violation is noted in the FAQ, but it seems
> worth noting as a serious bug since it means I can't use Torque objects as

> hash keys.
> 
> S.
> 
> 

-- 
Shevek                                    http://www.anarres.org/
I am the Borg.                         http://www.gothnicity.org/

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