/**
  * Interface for a stack: a collection of objects
  * that are inserted and removed according to the 
  * last-in first-out principle.
  * 
  * @author Roberto Tamassia
  * @author Michael Goodrich
  * @see StackEmptyException
  */

public interface Stack {
  /** @return number of elements in the stack. */
  public int size();

  /** @return true if the stack is empty, false otherwise. */
  public boolean isEmpty();

  /** 
   * @return top element in the stack.  
   * @exception StackEmptyException if the stack is empty. 
   */
  public Object top();

  /**
   * Insert an element at the top of the stack.
   * @param element element to be inserted.
   * @exception StackFullException if the stack is full.
   */
  public void push (Object element);

  /** 
   * Remove the top element from the stack.
   * @return element removed.
   * @exception StackEmptyException if the stack is empty.
   */
  public Object pop();
}