Thanks for your quick response Campbell.
In case of using the method with the List<T> argument I can call the add method for the list, but for the method with the List<?> argument I can not call the add method.
When calling add on List<?> the compiler shows some intriguing error message:
The method add(capture#1-of ?) in the type List<capture#1-of ?> is not applicable for the arguments (T)
So, it seems that the generic type T could not be used to add to the List<?> list. Checking my study guide shows that unbounded generics are immutable so it might be logical that you cannot call add on the List<?> but the error message don't give me a real clue.
I am still a bit confused about when using List<?> and List<T>....