public class GenericLinkedListBasedStack <Item> {
  
  private class Node {
    Item value;
    Node next;
    Node (Item theValue, Node theNext) {
      value = theValue;
      next = theNext;
    }
  }
  
  Node head = null;
  
  boolean isEmpty () {
    return (head == null);
  }
  
  void push (Item value) {
    head = new Node(value, head);
  }
  
  Item pop () {
    Item ret = head.value;
    head = head.next;
    return ret;
  }
}