Which types can be used for Java annotation members?

Question

Today I wanted to create my first annotation interface following this documentation and I got this compiler error

Invalid type for annotation member":
public @interface MyAnnotation {
    Object myParameter;
    ^^^^^^
}

Obviously Object cannot be used as type of an annotation member. Unfortunately I could not find any information on which types can be used in general.

This I found out using trial-and-error:

• String → Valid
• int → Valid
• Integer → Invalid (Surprisingly)
• String[] → Valid (Surprisingly)
• Object → Invalid

Perhaps someone can shed some light on which types are actually allowed and why.

Answer 1

It's specified by section 9.6.1 of the JLS. The annotation member types must be one of:

• primitive
• String
• an Enum
• another Annotation
• Class
• an array of any of the above

It does seem restrictive, but no doubt there are reasons for it.

Also note that multidimensional arrays (e.g. String[][]) are implicitly forbidden by the above rule.

Arrays of Class are not allowed as described in this answer.