What is the use of star(*) in yaml file?

Question

I was going through spring boot actuator when I stumbled upon this quote:

* has a special meaning in YAML, so be sure to add quotes if you want to include (or exclude) all endpoints.

I tried to look over the internet about it without any luck. What is the use of * in yaml file?

Answer 1

* is used to remove the repeated nodes. Consider this yaml example:

myprop:
  uid: &id XXX
myprop1:
  id: *id

The above will expand to:

myprop:
  uid: XXX
myprop1:
  id: XXX

Now try running this code:

@Value("${myprop.uid}") String uid;
@Value("${myprop1.id}") String id;

@Bean
ApplicationRunner runner() {
    return args -> {
        System.out.println(uid);  // prints "XXX"
        System.out.println(id); // prints "XXX"
        System.out.println(uid.equals(id)); // prints "true"
    };
}

From the spec:

Repeated nodes (objects) are first identified by an anchor (marked with the ampersand - “&”), and are then aliased (referenced with an asterisk - “*”) thereafter.