Java Generics for Upper bound & lower bound wild cards

I was reading java generics, I came across an interesting query. My question is as follows.

1. For an upper bounded wildcard

   public static void printList(List<? extends Number> list) {
       for (int i = 0; i < 10; i++) {
           list.add(i);// gives compilation error
       }
   }
   

2. For a lower bounded wildcard

   public static void printList(List<? super Integer> list) {
       for (int i = 0; i < 10; i++) {
           list.add(i);// successfully compiles
       }
   }
   

I am confused with this because looking at the Sun Oracle documentation I understand that the code should compile for point 1 as well

Upper Bound Wildcard Lower Bound Wildcard

Can anyone please help me to understand this?