多个注释

Question

Since it is not possible to have duplicated annotations on the same target, I'm working on a workaround for it. What I need is something likely to :

@Parent(sex="F", name="Alice")
@Parent(sex="M", name="Bob")
@Sibling(sex="M", name="Charlie")
@Sibling(sex="M", name="Dan")
@Sibling(sex="F", name="Eve")

I've though of adding another annotation @Relatives to contain them all, declaring the value member as an array of Relative annotations.

@Relatives({
    @Parent(sex="F", name="Alice")
    @Parent(sex="M", name="Bob")
    @Sibling(sex="M", name="Charlie")
    @Sibling(sex="M", name="Dan")
    @Sibling(sex="F", name="Eve")
})

However I can't define an array like that since @Parent and @Sibling @interfaces can't extend any @Relative superclass.

Is there any other way to do it apart from defining two different arrays Sibling[] siblings and Parent[] parents ? But that would create something like

@Relatives(
    parents={
        @Parent(sex="F", name="Alice"),
        @Parent(sex="M", name="Bob")
    }
    siblings={
        @Sibling(sex="M", name="Charlie")
        @Sibling(sex="M", name="Dan")
        @Sibling(sex="F", name="Eve")
   }
)

Answer 1

In 1.8 you have a half-baked way of repeatable annotations, see java.lang.annotation.Repeatable The trick is you still do need to declare your @Parents and @Siblings, but:

1. when using them, the containing annotations can be omitted

2. when scanning (introspecting) for them, you'll find your repeatable annotations inside their containing annotations ( @Parents and @Siblings ) in this case.

public @interface Parents {
      Parent[] value();
    }

    // this says: will be repeated inside a `Parents` nest
    @Repeatable(Parents.class) 
    public @interface Parent {
      String name();

      String sex() default "F";
    }

then you can

@Parent(sex="F", name="Alice"),
@Parent(sex="M", name="Bob")
Child firstChild;

See also "Repeating Annotations" on Oracles site