Compiler error: incompatible types

Question

When I try to compile this code it gives the error "incompatible types".
import java.util.ArrayList;
public class Poly {
     public static void main (String args[]) {
          Number integer = new Integer(1);
          ArrayList<Number> integers = new ArrayList<Integer>();
}Assigning a Number object an Integer which extends Number works fine.
But when I try to assign an ArrayList<Number> object an ArrayList<Integer> object it gives an imcompatible types error.
Shouldn't it work?
Edited by: aexyl93 on Jun 7, 2010 2:00 AM
Edited by: aexyl93 on Jun 7, 2010 2:05 AM

Answer 1

aexyl93 wrote:
Thanks for the quick replies.
I've never seen ArrayList<? extends obj> before.Nitpick: it's not "? extends obj" it's "? extends SomeClass".
"obj" kind of implies that you could use a variable/field here, which is wrong.
I thought it would be able to hold an object which extends what it's supposed to hold.A List<? extends Number> could contain any class that extends Number (as well as Number itself if it weren't an abstract class). However you can't add anything (except null), because you don't know the concrete type at this point.