code: public void printUsage() {
          String name = mainClass == null ? "<MainClass>" : mainClass.getName();
          String usage = "java " + name + " [OPTIONS]";
          final HelpFormatter formatter = new HelpFormatter();
          formatter.setWidth(120);
          formatter.printHelp(usage, options, true);
      }
docs: Prints the usage of the main class for this ArgParser.