code: public String next() {
          if (next == null)
              throw new NoSuchElementException();
          String replacement = replacementMap.get(next);
          replacement = (replacement == null) ? next : replacement;
          advance();
          return replacement;
      }
docs: Return the next token's replacement if such a replacement exists.  If no
  replacement for the next token exists, the original token is returned.
  
  @return The next token stored in this iterator, replaced with a
  subsituted value if one exists.