The Stack class is a subclass 
of Vector that implements a 
last-in-first-out (LIFO) object stack. The Stack 
class uses the following methods to provide stack behavior: 
- The push() method pushes 
an object onto the top of the stack. 
 
- The pop() method removes 
and returns the top element from the stack. If the stack is empty, pop() 
throws an EmptyStackException. 
 
- The peek() method returns, 
but does not remove, the top element from the stack. If the stack is empty, 
peek() throws an EmptyStackException. 
 
- The empty() method returns 
true if and only if the stack 
is empty.