code: private void updatePointer(long next_ptr, long next_value)
                      throws IOException,
                      EOFException {
          filemgr.seek(next_ptr);
          filemgr.writeLong(next_value);
      }
docs: ************************************************************************
  Seek to the "next" pointer for the HashtableEntry pointing to "me"
  because I've been reallocated.
  ***********************************************************************