Why can not I add an object of type Object into a List<?>?

Question

As far as I understand a List is definds as a list of some specific , yet unknown type . So whatever is the parameter type of this List

Answer 1

List listObj can point to any type of List that can store different kind of objects.

How do you think, would it be safe to let it add any objects if for example

List listObj = new ArrayList();
listObj.add(new Object());