1 /*
2 * Copyright (c) 2005, 2020, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package javax.lang.model.element;
27
28
29 import java.util.List;
30 import javax.lang.model.type.TypeMirror;
31 import javax.lang.model.util.*;
32
33 /**
34 * A visitor of the values of annotation type elements, using a
35 * variant of the visitor design pattern. Unlike a standard visitor
36 * which dispatches based on the concrete type of a member of a type
37 * hierarchy, this visitor dispatches based on the type of data
38 * stored; there are no distinct subclasses for storing, for example,
39 * {@code boolean} values versus {@code int} values. Classes
40 * implementing this interface are used to operate on a value when the
41 * type of that value is unknown at compile time. When a visitor is
42 * passed to a value's {@link AnnotationValue#accept accept} method,
43 * the <code>visit<i>Xyz</i></code> method applicable to that value is
44 * invoked.
45 *
46 * <p> Classes implementing this interface may or may not throw a
47 * {@code NullPointerException} if the additional parameter {@code p}
48 * is {@code null}; see documentation of the implementing class for
49 * details.
50 *
51 * <p> <b>WARNING:</b> It is possible that methods will be added to
52 * this interface to accommodate new, currently unknown, language
53 * structures added to future versions of the Java™ programming
54 * language. Therefore, visitor classes directly implementing this
55 * interface may be source incompatible with future versions of the
56 * platform. To avoid this source incompatibility, visitor
57 * implementations are encouraged to instead extend the appropriate
58 * abstract visitor class that implements this interface. However, an
59 * API should generally use this visitor interface as the type for
60 * parameters, return type, etc. rather than one of the abstract
61 * classes.
62 *
63 * <p>Note that methods to accommodate new language constructs could
64 * be added in a source <em>compatible</em> way if they were added as
65 * <em>default methods</em>. However, default methods are only
66 * available on Java SE 8 and higher releases and the {@code
67 * javax.lang.model.*} packages bundled in Java SE 8 were required to
68 * also be runnable on Java SE 7. Therefore, default methods
69 * were <em>not</em> used when extending {@code javax.lang.model.*}
70 * to cover Java SE 8 language features. However, default methods
71 * are used in subsequent revisions of the {@code javax.lang.model.*}
72 * packages that are only required to run on Java SE 8 and higher
73 * platform versions.
74 *
75 * @apiNote
76 *
77 * There are several families of classes implementing this visitor
78 * interface in the {@linkplain javax.lang.model.util util
79 * package}. The families follow a naming pattern along the lines of
80 * {@code FooVisitor}<i>N</i> where <i>N</i> indicates the
81 * {@linkplain javax.lang.model.SourceVersion source version} the
82 * visitor is appropriate for.
83 *
84 * In particular, a {@code FooVisitor}<i>N</i> is expected to handle
85 * all language constructs present in source version <i>N</i>. If
86 * there are no new language constructs added in version
87 * <i>N</i> + 1 (or subsequent releases), {@code
88 * FooVisitor}<i>N</i> may also handle that later source version; in
89 * that case, the {@link
90 * javax.annotation.processing.SupportedSourceVersion
91 * SupportedSourceVersion} annotation on the {@code
92 * FooVisitor}<i>N</i> class will indicate a later version.
93 *
94 * When visiting an annotation value representing a language construct
95 * introduced <strong>after</strong> source version <i>N</i>, a {@code
96 * FooVisitor}<i>N</i> will throw an {@link
97 * UnknownAnnotationValueException} unless that behavior is overridden.
98 *
99 * <p>When choosing which member of a visitor family to subclass,
100 * subclassing the most recent one increases the range of source
101 * versions covered. When choosing which visitor family to subclass,
102 * consider their built-in capabilities:
103 *
104 * <ul>
105 *
106 * <li>{@link AbstractAnnotationValueVisitor6
107 * AbstractAnnotationValueVisitor}s: Skeletal visitor implementations.
108 *
109 * <li>{@link SimpleAnnotationValueVisitor6
110 * SimpleAnnotationValueVisitor}s: Support default actions and a
111 * default return value.
112 *
113 * </ul>
114 *
115 * @param <R> the return type of this visitor's methods
116 * @param <P> the type of the additional parameter to this visitor's methods.
117 * @author Joseph D. Darcy
118 * @author Scott Seligman
119 * @author Peter von der Ahé
120 * @since 1.6
121 */
122 public interface AnnotationValueVisitor<R, P> {
123 /**
124 * Visits an annotation value.
125 * @param av the value to visit
126 * @param p a visitor-specified parameter
127 * @return a visitor-specified result
128 */
129 R visit(AnnotationValue av, P p);
130
131 /**
132 * A convenience method equivalent to {@code visit(av, null)}.
133 *
134 * @implSpec The default implementation is {@code visit(av, null)}.
135 *
136 * @param av the value to visit
137 * @return a visitor-specified result
138 */
139 default R visit(AnnotationValue av) {
140 return visit(av, null);
141 }
142
143 /**
144 * Visits a {@code boolean} value in an annotation.
145 * @param b the value being visited
146 * @param p a visitor-specified parameter
147 * @return the result of the visit
148 */
149 R visitBoolean(boolean b, P p);
150
151 /**
152 * Visits a {@code byte} value in an annotation.
153 * @param b the value being visited
154 * @param p a visitor-specified parameter
155 * @return the result of the visit
156 */
157 R visitByte(byte b, P p);
158
159 /**
160 * Visits a {@code char} value in an annotation.
161 * @param c the value being visited
162 * @param p a visitor-specified parameter
163 * @return the result of the visit
164 */
165 R visitChar(char c, P p);
166
167 /**
168 * Visits a {@code double} value in an annotation.
169 * @param d the value being visited
170 * @param p a visitor-specified parameter
171 * @return the result of the visit
172 */
173 R visitDouble(double d, P p);
174
175 /**
176 * Visits a {@code float} value in an annotation.
177 * @param f the value being visited
178 * @param p a visitor-specified parameter
179 * @return the result of the visit
180 */
181 R visitFloat(float f, P p);
182
183 /**
184 * Visits an {@code int} value in an annotation.
185 * @param i the value being visited
186 * @param p a visitor-specified parameter
187 * @return the result of the visit
188 */
189 R visitInt(int i, P p);
190
191 /**
192 * Visits a {@code long} value in an annotation.
193 * @param i the value being visited
194 * @param p a visitor-specified parameter
195 * @return the result of the visit
196 */
197 R visitLong(long i, P p);
198
199 /**
200 * Visits a {@code short} value in an annotation.
201 * @param s the value being visited
202 * @param p a visitor-specified parameter
203 * @return the result of the visit
204 */
205 R visitShort(short s, P p);
206
207 /**
208 * Visits a string value in an annotation.
209 * @param s the value being visited
210 * @param p a visitor-specified parameter
211 * @return the result of the visit
212 */
213 R visitString(String s, P p);
214
215 /**
216 * Visits a type value in an annotation.
217 * @param t the value being visited
218 * @param p a visitor-specified parameter
219 * @return the result of the visit
220 */
221 R visitType(TypeMirror t, P p);
222
223 /**
224 * Visits an {@code enum} value in an annotation.
225 * @param c the value being visited
226 * @param p a visitor-specified parameter
227 * @return the result of the visit
228 */
229 R visitEnumConstant(VariableElement c, P p);
230
231 /**
232 * Visits an annotation value in an annotation.
233 * @param a the value being visited
234 * @param p a visitor-specified parameter
235 * @return the result of the visit
236 */
237 R visitAnnotation(AnnotationMirror a, P p);
238
239 /**
240 * Visits an array value in an annotation.
241 * @param vals the value being visited
242 * @param p a visitor-specified parameter
243 * @return the result of the visit
244 */
245 R visitArray(List<? extends AnnotationValue> vals, P p);
246
247 /**
248 * Visits an unknown kind of annotation value.
249 * This can occur if the language evolves and new kinds
250 * of value can be stored in an annotation.
251 * @param av the unknown value being visited
252 * @param p a visitor-specified parameter
253 * @return the result of the visit
254 * @throws UnknownAnnotationValueException
255 * a visitor implementation may optionally throw this exception
256 */
257 R visitUnknown(AnnotationValue av, P p);
258 }