code: public static Md5Checksummer create()
      {
          String cname = System.getProperty(KEY);
          if (cname != null)
          {
              return createFromClassName(cname);
          }
          else
          {
              try
              {
                  return new Md5ChecksummerImpl();
              }
              catch (SecretShareException e)
              {
                  throw new SecretShareException("Failed to create built-in MD5 digest.  " +
                                                 "Use -D" + KEY + "=a.b.c.YourMd5Checksummer" +
                                                 " where your class must implement the interface " +
                                                 Md5Checksummer.class.getName(), e);
              }
  
          }
      }
docs: ==================================================