// An interface for a stack.
// Barry Cornelius, 19 June 2000
public interface Stack 
{
   // adds a new element (to the top of the target stack) that is
   // assigned the value pObject, a pointer to some object
   public void add(Object pObject);

   // returns a pointer to the object that is at the top element
   // of the target stack (without removing the element)
   public Object getFirst();

   // returns a pointer to the object that is at the top element
   // of the target stack and removes that element from the stack
   public Object remove();

   // returns the number of elements in the target stack
   public int size();

   // returns the value true if and only if the objects of the 
   // target stack and the stack passed as an argument have
   // the same values in the same order
   public boolean equals(Object pObject);

   // returns a hashcode value for the target stack
   public int hashCode();

   // returns a textual representation of the target stack
   public String toString();
}