public enum ElementType extends Enum<ElementType>

The constants of this enumerated class provide a simple classification of the syntactic locations where annotations may appear in a Java program. These constants are used in Target meta-annotations to specify where it is legal to write annotations of a given type.

The syntactic locations where annotations may appear are split into declaration contexts, where annotations apply to declarations, and type contexts, where annotations apply to types used in declarations and expressions.

The constants ANNOTATION_TYPE, CONSTRUCTOR, FIELD, LOCAL_VARIABLE, METHOD, PACKAGE, MODULE, PARAMETER, TYPE, and TYPE_PARAMETER correspond to the declaration contexts in JLS 9.6.4.1.

For example, an annotation whose interface is meta-annotated with @Target(ElementType.FIELD) may only be written as a modifier for a field declaration.

The constant TYPE_USE corresponds to the type contexts in JLS 4.11, as well as to two declaration contexts: class and interface declarations (including annotation declarations) and type parameter declarations.

For example, an annotation whose interface is meta-annotated with @Target(ElementType.TYPE_USE) may be written on the class or interface of a field (or within the class or interface of the field, if it is a nested or parameterized class or interface, or array class), and may also appear as a modifier for, say, a class declaration.

The TYPE_USE constant includes class and interface declarations and type parameter declarations as a convenience for designers of type checkers which give semantics to annotation interfaces. For example, if the annotation interface NonNull is meta-annotated with @Target(ElementType.TYPE_USE), then @NonNull class C {...} could be treated by a type checker as indicating that all variables of class C are non-null, while still allowing variables of other classes to be non-null or not non-null based on whether @NonNull appears at the variable's declaration.