This passes compilation:
LinkedList list1 = new LinkedList ();
This doesn't:
LinkedList
i.e. a LinkedList variable can be assigned any LinkedList. A LinkedList variable can only be assigned a LinkedList (or a raw LinkedList, which is not advised to use).
On the other hand the following add:
LinkedList list1 = new LinkedList ();
list1.add("x");
doesn't pass compilation, while the following does:
LinkedList
