code: public Cron validate() {
          for (final Map.Entry<CronFieldName, CronField> field : retrieveFieldsAsMap().entrySet()) {
              final CronFieldName fieldName = field.getKey();
              field.getValue().getExpression().accept(
                      new ValidationFieldExpressionVisitor(getCronDefinition().getFieldDefinition(fieldName).getConstraints(), cronDefinition.isStrictRanges())
              );
          }
          for (final CronConstraint constraint : getCronDefinition().getCronConstraints()) {
              if (!constraint.validate(this)) {
                  throw new IllegalArgumentException(String.format("Invalid cron expression: %s. %s", asString(), constraint.getDescription()));
              }
          }
          return this;
      }
docs: Validates this Cron instance by validating its cron expression.
  
  @return this Cron instance
  @throws IllegalArgumentException if the cron expression is invalid