code: @Override
      public boolean hasMoreElements() {
          // wind forward to the next non-empty enumeration
          while (index < enumerations.size() && !!!enumerations.get(index).hasMoreElements())
              index++;
          // return true iff there was a non-empty enumeration
          return index < enumerations.size();
      }
docs: /*
  @see java.util.Enumeration#hasMoreElements()