A linear data structure is one in which each element has a unique predecessor
and a unique successor.  There will at most one element without a predecessor
(the first) and at most one element without a successor (the last).

A stack is a linear data structure in which insertions and deletions are done
at one end.  The end where the insertions and deletions take place is called the
top.  An insertion into a stack is called a push, and a deletion is called a
pop.
	
	The ADT of a stack is:

Members:  A list of items with a position top that indicates the top of the stack,
       where insertions and deletions are to be done.

Methods:

Constructor:
Input:		None
Precondition:	int
Process:	Initialize the top of the stack so that it is empty. Set the
		value of size to be the passed value, and create an array of
		that size.
Output:		None
Postcondition:	The stack is now empty.

StackEmpty:
Input:		None
Precondition:	None
Process:	Check whether the stack is empty.
Output:		Return TRUE is the stack is empty, FALSE otherwise.
Postcondition:	None

StackFull:
Input:		None
Precondition:	None
Process:	Check whether the stack is full.
Output:		Return TRUE is the stack is full, FALSE otherwise.
Postcondition:	None

Pop:
Input:		None
Precondition:	Stack is not empty.
Process;	Remove the item from the top of the stack.
Output:		Return the element from the top of the stack.
Postcondition:	Element at the top of they stack is removed

Push:
Input:		An item for the stack.
Precondition:	Stack is not full.
Process:	Store the item on the top of the stack.
Output:		None.
Postcondition:	The stack has a new element at the top.

Peek:
Input:		none
Precondition:	Stack is not empty.
Process:	Retrieve the value of the item at the top of the stack.
Output:		Return the value at the top of the stack.
Postcondition:	none

Search:
Precondition:	none
Input:		An item to be searched for
Process:	Search the stack for the item.  If it is at the top of the stack
		return 1, the second item on the stack, return 2, etc.  If it is
		not in the stack, return -1.
Output:         int, the relative position in the stack.
Postcondition:  none

Note: The implementation of a stack in java.util.Stack does not have a method
of StackFull.