import java.util.Stack;


public class stackApplication {

   public static void main(String[] args) {
      Stack s = new Stack();

      if (s.isEmpty()) System.out.println("stack is empty");

      s.push(new Integer(5)); s.push(new Integer(-2));
      s.push(new Integer(1)); s.push(new Integer(99));

      if (s.isEmpty()) System.out.println("stack is empty");

      while (!s.isEmpty()) {
         System.out.println("top of stack value is : "+s.peek());
         s.pop();  /* discard the return value from pop() */
      }

      System.out.println("Stack empty,  exiting ...");

   }

}

interface StackInterface {

   /* returns true if stack is empty, true otherwise */
   public boolean isEmpty() ;

   /* return true if stack is full, false otherwise */
   public boolean isFull();

   /* adds object to stack if stack is not full (let the user beware!) */
   public void push(Object x);

   /* removes and returns object at the top of the stack,
        fails (ungracefully) if the stack is empty  */
   public Object pop();

   /* returns object at the top of the stack,
        fails (ungracefully) if the stack is empty  */
   public Object peek();
  
}

class xStack implements StackInterface {
	   /* returns true if stack is empty, true otherwise */
   public boolean isEmpty() {return true;}

   /* return true if stack is full, false otherwise */
   public boolean isFull() { return false;}

   /* adds object to stack if stack is not full (let the user beware!) */
   public void push(Object x) {return;}

   /* removes and returns object at the top of the stack,
        fails (ungracefully) if the stack is empty  */
   public Object pop() {return null;}

   /* returns object at the top of the stack,
        fails (ungracefully) if the stack is empty  */
   public Object peek() {return null;}
}