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From "Carsten Ziegeler" <cziege...@s-und-n.de>
Subject RE: [RT]: Calculating the cache key
Date Tue, 28 May 2002 08:22:13 GMT

Carsten Ziegeler wrote:
> 
> Volker Schmitt wrote:
> > 
> > Hi,
> > 
> > the current Interface of CacheableProcessingComponent:
> > 
> > <snip>
> > 
> > why not using Object as a return value of "generateKey" ? I think 
> > this is more
> > flexible and allows the implementation of Compound keys.
> > 
> Yes, I thought about this over the weekend, too. Object as the return
> value is the most flexible.
> 
> But when using Object the caching algorithm is required to build
> compound objects (arrays etc.) and cannot use simple string operations 
> for building the compound key anymore. (Or the Object must implement
> a reliable toString() method)
> 
> While building a compound object with for example an array is a simple
> solution, I see currently a problem in storing this into the cache.
> The cache can for example be implemented as a hash table, so the
> compound key object must somehow implement hashCode() and equals().
> While equals() can be easily implemented, I see no good solution for
> hashCode().
> Do you know a solution for this?
> 

I looked at the docs of the hash table and it seems that a hashCode
computation is not so difficult: If two objects are equal they must
have the same hash code. If the hash code differs, they are not equal.
But if the hash code is the same, the objects must not necessarily
the same.
Ok, I give this a try and changed the type of the key from String to
Serializable (and not to Object). Let's see if I can get this working
today...

Regards
Carsten 

Carsten Ziegeler     Chief Architect     Open Source Group, S&N AG
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