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

[Joe Darcy]

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.

-Joe