Interfaces - The Java Language Specification - page 280

String synopsis(); // Synopsis of RFE
String engineer(); // Name of engineer who implemented RFE
String date();

// Date RFE was implemented

}

The following annotation type declaration defines an annotation type with no ele-
ments, termed a marker annotation type :
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/**
* An annotation with this type indicates that the
* specification of the annotated API element is
* preliminary and subject to change.
*/
@interface Preliminary {}

It is a compile-time error if the return type of a method declared in an annotation type is not
one of the following: a primitive type, String , Class , any parameterized invocation of Class ,
an enum type (§ 8.9 ) , an annotation type, or an array type (§10) whose element type is one
of the preceding types.

This specification precludes elements whose types are nested arrays. For example,
this annotation type declaration is illegal:

@interface Verboten {
String[][] value();

}

It is a compile-time error if any method declared in an annotation type has a signature that
is override-equivalent to that of any public or protected method declared in class Object or in
the interface java.lang.annotation.Annotation .

It is a compile-time error if an annotation type declaration T contains an element of type T ,
either directly or indirectly.

For example, this is illegal:

@interface SelfRef { SelfRef value(); }

and so is this:

@interface Ping { Pong value(); }
@interface Pong { Ping value(); }