/** Delivers next (i.e., first undelivered) value from input key-value pairs */
 public String next() throws NoSuchElementException {
   if (!hasNext()) throw new NoSuchElementException("No more key-value pairs for this key");
   String value = WmrReducerImpl.nextValue;
   WmrReducerImpl.advance();
   return value;
 }
 public boolean hasNext() {
   return !WmrReducerImpl.endInput() && (WmrReducerImpl.nextKey.equals(myKey));
 }