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 the 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 9.7 of the JLS. The annotation member types must be one of:

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

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

Answer 2

I agree with Skaffman for the Types available.

Additional restriction : it has to be a compile-time constant.

For example, the following are forbidden:

    @MyAnnot("a" + myConstantStringMethod())
    @MyAnnot(1 + myConstantIntMethod())