code: protected final int index (String source, String prefix, int lineno)
          throws CDDBException
      {
          int eidx = source.indexOf("=", prefix.length());
          if (eidx == -1) {
              throw new CDDBException(500, "Malformed line '" + source + "' number " + lineno);
          }
  
          try {
              return Integer.parseInt(source.substring(prefix.length(), eidx));
          } catch (NumberFormatException nfe) {
              throw new CDDBException(500, "Malformed line '" + source + "' number " + lineno);
          }
      }
docs: Extracts the track index of the supplied line (the number immediately following the supplied
  prefix and preceding the equals sign) or throws a CDDBException if the line contains no
  equals sign or track index.