code: public static String getExt(final String aFileName) {
          final int index = aFileName.lastIndexOf(DOT);
  
          if (index != -1) {
              return aFileName.substring(index + 1, aFileName.length());
          }
  
          return "";
      }
docs: Returns a file extension (as delimited by a period).
  
  @param aFileName A file name from which to get the extension
  @return The extension or an empty string if the file doesn't have an extension