code: private static Constructor<? extends OptionHandler> getConstructor(Class<? extends OptionHandler> handlerClass) {
          try {
              return handlerClass.getConstructor(CmdLineParser.class, OptionDef.class, Setter.class);
          } catch (NoSuchMethodException e) {
              throw new IllegalArgumentException(Messages.NO_CONSTRUCTOR_ON_HANDLER.format(handlerClass));
          }
      }
docs: Finds the constructor for an option handler.