code: public static String camelCaseToUnderscore(final String camelCaseString) {
  
          final StringBuilder sb = new StringBuilder();
          for (final String camelPart : camelCaseString.split("(?<!(^|[A-Z]))(?=[A-Z])|(?<!^)(?=[A-Z][a-z])")) {
              if (sb.length() > 0) {
                  sb.append(CASE_SEPARATOR);
              }
              sb.append(camelPart.toUpperCase(Locale.getDefault()));
          }
          return sb.toString();
      }
docs: Convert aStringUnderscored into A_STRING_UNDESCORED.
  
  @param camelCaseString the string to convert
  
  @return the underscored string