Re: Generics warning message.
- From: External Concepts Guild <REE9opdZ@xxxxxxxxx>
- Date: Mon, 31 Dec 2007 08:07:29 -0800 (PST)
On Dec 30, 8:12 pm, Lew <l...@xxxxxxxxxxxxx> wrote:
External Concepts Guild wrote:
There might be a way. I think the following code performs a similar
function to what you are trying to achieve. The code compiles without
warnings or errors and it runs correctly. Nonetheless, it leaves
something to be desired.
private static < R > ArrayList < R > nowarningCast
( Class < R > clazz , ArrayList in )
{
ArrayList < R > out = new ArrayList < R > ( ) ;
for ( Object val : in )
{
R r = clazz . cast ( val ) ;
out . add ( r ) ;
}
return ( out ) ;
}
}
That's not a cast, that's a copy. But I'll bet you could do a cast with a
Class<ArrayList<R>> with a similar idiom.
--
Lew
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You are absolutely correct: it is a copy not a cast. I believe that
because of the nature of type erasure <http://java.sun.com/docs/books/
tutorial/java/generics/erasure.html> it is impossible to do a cast
(without at least generating a warning). Thus to achieve the effect
that the OP desires, it is necessary to cheat (e.g. copying rather
than casting).
If you have control of the writing operation as well as the reading,
then you could solve this problem by using a nonparameterized
extension of ArrayList<R>. For example, consider class MyArrayList
extends ArrayList<String> { }. If you wrote a MyArrayList, then you
should be able to read it and cast it without warnings.
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.
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