Help me understand these generic method warnings
- by Raj
Folks,
I have a base class, say:
public class BaseType { private String id; ... }
and then three subclasses:
public class TypeA extends BaseType { ... }
public class TypeB extends BaseType { ... }
public class TypeC extends BaseType { ... }
I have a container class that maintains lists of objects of these types:
public class Container
{
private List<TypeA> aList;
private List<TypeB> bList;
private List<TypeC> cList;
// finder method goes here
}
And now I want to add a finder method to container that will find an object from one of the lists. The finder method is written as follows:
public <T extends BaseType> T find( String id, Class<T> clazz )
{
final List<T> collection;
if( clazz == TypeA.class )
{
collection = (List<T>)aList;
}
else if( clazz == TypeB.class )
{
collection = (List<T>)bList;
}
else if( clazz == TypeC.class )
{
collection = (List<T>)cList;
}
else return null;
for( final BaseType value : collection )
{
if( value.getId().equals( id ) )
{
return (T)value;
}
}
return null;
}
My question is this: If I don't add all the casts to T in my finder above, I get compile errors. I think the compile should be able to infer the types based on parametrization of the generic method (). Can anyone explain this?
Thanks.
-Raj
