code: private static void checkSrcOption(String[] args)
          throws ProblemException {
          Set<File> dirs = new HashSet<File>();
          for (int i = 0; i<args.length; ++i) {
              if (args[i].equals("-src")) {
                  if (i+1 >= args.length) {
                      throw new ProblemException("You have to specify a directory following -src.");
                  }
                  StringTokenizer st = new StringTokenizer(args[i+1], File.pathSeparator);
                  while (st.hasMoreElements()) {
                      File dir = new File(st.nextToken());
                      if (!dir.exists()) {
                          throw new ProblemException("This directory does not exist: "+dir.getPath());
                      }
                      if (!dir.isDirectory()) {
                          throw new ProblemException("\""+dir.getPath()+"\" is not a directory.");
                      }
                      if (dirs.contains(dir)) {
                          throw new ProblemException("The src directory \""+dir.getPath()+"\" is specified more than once!");
                      }
                      dirs.add(dir);
                  }
              }
          }
          if (dirs.isEmpty()) {
              throw new ProblemException("You have to specify -src.");
          }
      }
docs: Check the -src options.