Linked Lists 4: The Empty List (null)

number of data values	number of nodes
3	3
2	2
1	1
0	0

null signifies "the empty list"

A recursive definition of a linked list:
* null
* a node whose next refers to a linked list

Why Linked Lists?
* Linked list are BEAUTIFUL.
* Linked lists are more efficient than arrays/ArrayLists in some situations
* Linked lists provide a foundation for understanding other node-based data structures (trees, graphs)