Java Generics question

Hi

I'm studying for the SCJP 5.0 and have a question about Generic
Collections.

The question is, If I use wildcards in a collection then I can't use
the add() method for the collection (ArrayList in this example). I can
use a wildcarded ArrayList to asign other ArrayLists to this but what
is the big purpose of this?

Can anybody explain that to me, help would be very apreciated.

-------------------------- Code Example --------------------------
import java.util.*;
public class AnimalGenericTester {

  public AnimalGenericTester() {
    ArrayList<Animal> myList = new ArrayList<Animal>();
    myList.add(new Dog());
    myList.add(new Cat());
    printAnimal(myList);
  }

  void printAnimal(ArrayList<? super Cat> list) {
    //What is the purpose of this???
    //The myList now contains a Dog and a Cat but Dog is NOT a super of
cat
    //I really can't see the point of this generic functionality
  }

  public static void main(String[] args) {
    new AnimalGenericTester();
  }

}

abstract class Animal {
  abstract void checkup();

}

class Dog extends Animal {
  void checkup() {
    System.out.println("Dog");
  }

}

class Cat extends Animal {
  void checkup() {
    System.out.println("Cat");
  }

}

-------------------------- END OF Code Example
--------------------------