Collections of generics
- by Luis Sep
According to what I've read, I think this can't be done, but I'd like to be sure.
I have a class OpDTO and several other *DTO extends OpDTO.
Then, I want to have a method to extract just certain elements from lists of these child DTOs, and return the extracted elements in another list:
public List<? extends OpDTO> getLastOp (List<? extends OpDTO> listDTOs) {
List<? extends OpDTO> last = new ArrayList<? extends OpDTO>(); //compile error: Cannot instantiate the type ArrayList<? extends OpDTO>
//processing
return last;
}
I want ult to be a list of elements of the same kind as elements in listDTOs, and use only OpDTO's methods, but it produces a compile error:
Cannot instantiate the type ArrayList<? extends OpDTO>
I also tried doing something like:
public <T> List<T> getLastOp (List<T> listDTOs) {
List<T> last = new ArrayList<T>();
//processing
return last;
}
But then I can't enforce elements in listDTOs to be a subclass of OpDTO, and can't instantiate T.
Any idea?
