/**
  * Specifies that the given set of options are mutually-exclusive. Only one of the given options
  * will be selected. The parser ignores all but the last of these options.
  */
 public CommandLineParser allowOneOf(String... options) {
   Set<CommandLineOption> commandLineOptions = new HashSet<CommandLineOption>();
   for (String option : options) {
     commandLineOptions.add(optionsByString.get(option));
   }
   for (CommandLineOption commandLineOption : commandLineOptions) {
     commandLineOption.groupWith(commandLineOptions);
   }
   return this;
 }