Let say i have a method: void write(List list) and i call this with
a List list,write(list) and trying to add in write() like
list.add(new Dog()) is a compilation error, why?
? is a wildcard operator in generics, now what it means is that you don't exactly know what kind of List you are getting. So how can you be sure that it can be a List of Dogs. If it was a List<Cat> then your write method would have added a Dog to it. So Java restricts you from doing that.
Now, if i use bounded wild cards, write(List list> it
solves the above problem, why?
? super Dog stands for any super class of Dog including itself. So when you get a List<? super Dog> in write you know that the List is a list of either List<Object> or List<Dog>. In both cases it is safe to add a new Dog to the list.
