Abstract Data Type (ADT):
   A specification of a collection of data and the
   operations that can be performed on it.
   
   Describes what a collection does, not how it does it.


    interface            implementation
List<String> list = new ArrayList<String>();
   
   
"You should favor the use of interfaces over classes to refer to objects. 
 If appropriate interface types exist, then parameters, return values, 
 variables and fields should all be declared using interface types.
 The only time you really need to refer to an object's class is when you're 
 creating it with a constructor."
                                                      -Joshua Bloch


Stack:
   LIFO (last in, first out) data structure
   example: cafeteria trays

   Stack<E> s = new Stack<E>() - makes an empty stack
   public void push(E value)   - adds to the top of the stack
   public E pop()              - removes from the top of the stack
   public boolean isEmpty()    - true if empty, false otherwise
   public int size()           - number of elements in the stack

Queue:
   FIFO (first in, last out) data structure
   example: checkout lines

   Queue<E> q = new LinkedList<E>() - makes an empty queue
   public void add(E value)         - adds to the back of the queue
   public E remove()                - removes from the front of the queue
   public boolean isEmpty()         - true if empty, false otherwise
   public int size()                - number of elements in the queue