[jboss-dev] generic collection item type

[Adrian]

On Mon, 2007-07-30 at 14:39 +0200, Alexey Loubyansky wrote:
> That's my problem. How can I find out using the API which parameter is 
> passed to the Collection
> 
>     public abstract class CollectionClass<T1 extends Object, T2 extends 
> Object, T3 extends Object>
>        implements Comparable<T2>, Collection<T1>, java.util.Comparator<T3>
>     {
>     }
> 
> Besides that I have to keep track of arguments from sub- to super 
> classes. And Collection interface can be extended implemented on 
> different levels with different type parameters (but those should belong 
> to the same type hierarchy).
> But the main problem I think is the first one above.

That's a very good question. If the class implements
Collection<Whatever> directly, you can get at this
information.

It's just:

for (ClassInfo intf : myClass.getInterfaces())
{
   if (intf.getName().equals(Collection.class.getName())
     return intf.getActualTypeArguments()[0];
}

But if it is on a superclass, there is no way to get
at this information.

In the main java reflection api:

Class.getGenericSuperClass() returns a ParameterizedType

but from that ParameterizedType there is no route
to get the generic interfaces.

e.g.
public class MyClass extends AbstractCollection<Whatever>

then there's no way to get at the ParameterizedType
Collection<Whatever> that AbstractCollection<Whataver> implements.

What would really be useful would be if there was a
Class.getAllGenericInterfaces();
but that doesn't exist.


-- 
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Adrian Brock
Chief Scientist
JBoss, a division of Red Hat
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