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25 
26 package java.lang.annotation;
27 
28 /**
29  * The constants of this enumerated type provide a simple classification of the
30  * syntactic locations where annotations may appear in a Java program. These
31  * constants are used in {@link Target java.lang.annotation.Target}
32  * meta-annotations to specify where it is legal to write annotations of a
33  * given type.
34  *
35  * <p>The syntactic locations where annotations may appear are split into
36  * <em>declaration contexts</em> , where annotations apply to declarations, and
37  * <em>type contexts</em> , where annotations apply to types used in
38  * declarations and expressions.
39  *
40  * <p>The constants {@link #ANNOTATION_TYPE} , {@link #CONSTRUCTOR} , {@link
41  * #FIELD} , {@link #LOCAL_VARIABLE} , {@link #METHOD} , {@link #PACKAGE} ,
42  * {@link #PARAMETER} , {@link #TYPE} , and {@link #TYPE_PARAMETER} correspond
43  * to the declaration contexts in JLS 9.6.4.1.
44  *
45  * <p>For example, an annotation whose type is meta-annotated with
46  * {@code @Target(ElementType.FIELD)} may only be written as a modifier for a
47  * field declaration.
48  *
49  * <p>The constant {@link #TYPE_USE} corresponds to the 15 type contexts in JLS
50  * 4.11, as well as to two declaration contexts: type declarations (including
51  * annotation type declarations) and type parameter declarations.
52  *
53  * <p>For example, an annotation whose type is meta-annotated with
54  * {@code @Target(ElementType.TYPE_USE)} may be written on the type of a field
55  * (or within the type of the field, if it is a nested, parameterized, or array
56  * type), and may also appear as a modifier for, say, a class declaration.
57  *
58  * <p>The {@code TYPE_USE} constant includes type declarations and type
59  * parameter declarations as a convenience for designers of type checkers which
60  * give semantics to annotation types. For example, if the annotation type
61  * {@code NonNull} is meta-annotated with
62  * {@code @Target(ElementType.TYPE_USE)}, then {@code @NonNull}
63  * {@code class C {...}} could be treated by a type checker as indicating that
64  * all variables of class {@code C} are non-null, while still allowing
65  * variables of other classes to be non-null or not non-null based on whether
66  * {@code @NonNull} appears at the variable's declaration.
67  *
68  * @author  Joshua Bloch
69  * @since 1.5
70  * @jls 9.6.4.1 @Target
71  * @jls 4.1 The Kinds of Types and Values
72  */
73 public enum ElementType {
74     /** Class, interface (including annotation type), or enum declaration */
75     TYPE,
76 
77     /** Field declaration (includes enum constants) */
78     FIELD,
79 
80     /** Method declaration */
81     METHOD,
82 
83     /** Formal parameter declaration */
84     PARAMETER,
85 
86     /** Constructor declaration */
87     CONSTRUCTOR,
88 
89     /** Local variable declaration */
90     LOCAL_VARIABLE,
91 
92     /** Annotation type declaration */
93     ANNOTATION_TYPE,
94 
95     /** Package declaration */
96     PACKAGE,
97 
98     /**
99      * Type parameter declaration
100      *
101      * @since 1.8
102      */
103     TYPE_PARAMETER,
104 
105     /**
106      * Use of a type
107      *
108      * @since 1.8
109      */
110     TYPE_USE
111 }
112