code: public static void acceptsFile(OptionParser parser) {
          parser.acceptsAll(Arrays.asList(OPT_F, OPT_FILE), "file path for input/output")
                .withRequiredArg()
                .describedAs("file-path")
                .ofType(String.class);
      }
docs: Adds OPT_F | OPT_FILE option to OptionParser, with one argument.
  
  @param parser OptionParser to be modified
  @param required Tells if this option is required or optional