[Fwd: Code review request: 7072353 JNDI libraries do not build with javac -Xlint:all -Werror]

[Dr Andrew John Hughes]

On 09:24 Wed 03 Aug     , Joe Darcy wrote:
> On 8/3/2011 12:42 AM, David Holmes wrote:
> > Alexandre Boulgakov said the following on 08/03/11 04:44:
> >> On 8/2/2011 2:19 AM, Xuelei Fan wrote:
> >>> 3017 Vector<Object>  temp = (Vector)extractURLs(res.errorMessage);
> >>>     You may not need the conversion any more, the return value of
> >>> extractURLs() has been updated to
> >>>     2564     private static Vector<String>  extractURLs(String 
> >>> refString)
> >> The cast is needed to go from Vector<String> to Vector<Object>.
> >
> > Raw types should be avoided (here and elsewhere there are casts to raw 
> > Vector). I'm surprised (generics continue to surprise me) that despite 
> > all our advances in type-inference etc that the compiler can not tell 
> > that a Vector<T> is-a Vector<Object>. :(
> 
> That is because in general a Vector<T> is not a Vector<Object> because 
> of the way subtyping works.  As with arrays, it all looks fine until you 
> want to change the container; consider
> 
> Vector<String> vs = new Vector<>();
> ...
> Vector<Object> vo = vs; // Assume this was okay to alias an object 
> vector and a string vector
> 
> vo.add(new Integer(1));  // Add an Integer to a list of strings, boom!
> 
> Using wildcards makes the subtyping work along the type argument axis.
> 

Exactly.  What I wondered on reading this is why it needs to be cast to a
Vector<Object> anyway.  That would only reduce type safety as you say.

> -Joe
> 

-- 
Andrew :)

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Red Hat, Inc. (http://www.redhat.com)

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