On 8/3/2011 10:51 AM, Dr Andrew John Hughes wrote:
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.
The current code uses it to store Strings and Vector<String>s. The most
specific common base type is Object, so I don't think we can do any
better than that.
-Joe
