code: private Entry find(int index) // throws IndexOutOfBoundsException
      {
          // if (index < 0 || index > size())
          // throw new IndexOutOfBoundsException();
  
          // System.out.print("find: " + index + " (");
          for (Entry entry = head; entry != null; entry = entry.getNext()) {
              // System.out.print(entry.getIndex() + ":" + entry.getValue() +
              // " ");
              if (entry.getIndex() == index)
                  return entry;
          } // end for
  
          // System.out.print(")\n");
          return null;
      }
docs: Returns the <code>Entry</code> specified by this index
  
  @param index
  index of element to return.
  @return an <code>Entry</code> if and only if the index exists;
  <code>null</code> otherwise