private static Node insertRecursive(Node headNode, 
                        java.lang.Comparable newItem) {
  if ( (headNode == null) ||        (newItem.compareTo(headNode.getItem()) < 0) ) {
    // base case: insert newItem at the beginning of the
    // linked list that nextNode references
    Node newNode = new Node(newItem, headNode);
    headNode = newNode;
  } 
  else { //insert into rest of linked list
    Node nextNode = insertRecursive(headNode.getNext(),newItem);
    headNode.setNext(nextNode);
  } // end if
  return headNode;
}  // end insertRecursive