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From Emmanuel Lecharny <>
Subject [Return of the clones]
Date Sat, 27 Oct 2007 21:03:49 GMT
David Jencks wrote:
> On Oct 27, 2007, at 11:56 AM, Alex Karasulu wrote:
>> Hi Emmanuel, and others,
>> I was taking another look at these ServerEntry interfaces etc and 
>> noticed that you define
>> the clone() method as supported within the interfaces themselves.
>> I may be wrong but I've always tried to avoid defining the clone() 
>> method in interfaces and
>> have gone to great lengths to avoid using the clone() method.  I 
>> prefer to use factories or
>> constructors instead.  For me the clone operation is scary and leads 
>> to a lot of confusion.
>> Most of the time unless I have to support it because of a class I'm 
>> extending I will deal with
>> it but when I can I try to avoid it.
>> Emmanuel was wondering if you see supporting clone() as critical and 
>> recommend we keep
>> it?
>> I know just having a feeling is not enough to say using clone is 
>> dangerous but I've always ran
>> into issues with it and the variance in the semantics to the point 
>> where dealing with it was not
>> worth the trouble.
>> Please could anyone with a clearer understanding of the pros and cons 
>> provide some further
>> guidance on this topic?
> I doubt I have a clearer understanding but Joshua Bloch's Effective 
> Java has 8 pages pointing out how hard it is to write clone methods 
> correctly and the problems they cause and how copy constructors or 
> factory methods have much clearer semantics and implementations.  I 
> never feel like I know what is going to happen when I call clone :-)

Beside being the worst episode of Star Wars, I wouls say that clone is 
not my favorite Java feature, but I used it a couple of times without 
problems. The rules I have adopted were pretty simple : if it start to 
be complex, stop using clone... In fact, when it's strait forward, like 
you have a flat object, or a very simple inheritance scheme, clone() is 
an option. Otherwise, a good factory or copy() constructor is the way to 

When performance is an issue, then clone may become a candidate, but 
with a lot of caution...

E.clone() (or is it E.clown() ? ;)

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