Difference between * and ? in Spring @Scheduled(cron=".....")

Question

I've been looking at the Spring Boot example for scheduling tasks (https://spring.io/guides/gs/scheduling-tasks/) and reading through some documentation (https://javahunter.wordpress.com/2011/05/05/cronscheduler-in-spring/) and I see that * and ? are used almost interchangeably.

For example, the line

@Scheduled(cron = "0 15 10 ? * *") 

and

@Scheduled(cron = "0 15 10 * * ?") 

do the exact same thing. So what is the difference between * and ?

Answer 1

The tutorial is outdated. The symbol ? means exactly the same as the symbol *.

As of Spring version 3.1.2.RELEASE, the call hierarchy is the following:

1. The constructor CronTrigger(String) calls the constructor CronSequenceGenerator(String)
2. CronSequenceGenerator(String) calls parse(String)
3. parse(String) calls setDays(BitSet bits, String field, int max).

Its implementation is clear:

private void setDays(BitSet bits, String field, int max) {     if (field.contains("?")) {         field = "*";     }     setNumberHits(bits, field, 0, max); } 

So, if ?, then *.

Answer 2

asterix stands for all possible values. question marks should be used for non specific value

*("all values") - used to select all values within a field. For example, "" in the minute field means *"every minute".

? ("no specific value") - useful when you need to specify something in one of the two fields in which the character is allowed, but not the other. For example, if I want my trigger to fire on a particular day of the month (say, the 10th), but don't care what day of the week that happens to be, I would put "10" in the day-of-month field, and "?" in the day-of-week field. See the examples below for clarification.

Copied from the tutorial