TreeSet<Integer> getSet(int type) {
        switch (type) {
            case SECOND:
                return seconds;
            case MINUTE:
                return minutes;
            case HOUR:
                return hours;
            case DAY_OF_MONTH:
                return daysOfMonth;
            case MONTH:
                return months;
            case DAY_OF_WEEK:
                return daysOfWeek;
            case YEAR:
                return years;
            default:
                return null;
        }
    }
Indicates whether the specified cron expression can be parsed into a
valid cron expression

@param cronExpression the expression to evaluate
@return a boolean indicating whether the given expression is a valid cron
        expression
server/core/src/main/java/com/ke/schedule/server/core/common/CronExpression.java