code: public static void checkOperatorIsValid(int operatorCode) {
          switch (operatorCode) {
              case OPERATOR_LT:
              case OPERATOR_LE:
              case OPERATOR_EQ:
              case OPERATOR_NE:
              case OPERATOR_GE:
              case OPERATOR_GT:
              case OPERATOR_UNKNOWN:
                  return;
              default:
                  throw new IllegalStateException(String.format(Locale.US, ERROR_INVALID_CODE, operatorCode));
          }
      }
docs: Checks if the given operator code is a valid one.
  
  @param operatorCode an operator code to evaluate
  @throws IllegalStateException if operatorCode is not a known operator code.