1 /*
2 * Copyright (c) 2005, 2017, 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
31 import javax.lang.model.type.TypeMirror;
32
33
34 /**
35 * A visitor of the values of annotation type elements, using a
36 * variant of the visitor design pattern. Unlike a standard visitor
37 * which dispatches based on the concrete type of a member of a type
38 * hierarchy, this visitor dispatches based on the type of data
39 * stored; there are no distinct subclasses for storing, for example,
40 * {@code boolean} values versus {@code int} values. Classes
41 * implementing this interface are used to operate on a value when the
42 * type of that value is unknown at compile time. When a visitor is
43 * passed to a value's {@link AnnotationValue#accept accept} method,
44 * the <code>visit<i>Xyz</i></code> method applicable to that value is
45 * invoked.
46 *
47 * <p> Classes implementing this interface may or may not throw a
48 * {@code NullPointerException} if the additional parameter {@code p}
49 * is {@code null}; see documentation of the implementing class for
50 * details.
51 *
52 * <p> <b>WARNING:</b> It is possible that methods will be added to
53 * this interface to accommodate new, currently unknown, language
54 * structures added to future versions of the Java™ programming
55 * language. Therefore, visitor classes directly implementing this
56 * interface may be source incompatible with future versions of the
57 * platform. To avoid this source incompatibility, visitor
58 * implementations are encouraged to instead extend the appropriate
59 * abstract visitor class that implements this interface. However, an
60 * API should generally use this visitor interface as the type for
61 * parameters, return type, etc. rather than one of the abstract
62 * classes.
63 *
64 * <p>Note that methods to accommodate new language constructs could
65 * be added in a source <em>compatible</em> way if they were added as
66 * <em>default methods</em>. However, default methods are only
67 * available on Java SE 8 and higher releases and the {@code
68 * javax.lang.model.*} packages bundled in Java SE 8 were required to
69 * also be runnable on Java SE 7. Therefore, default methods
70 * were <em>not</em> used when extending {@code javax.lang.model.*}
71 * to cover Java SE 8 language features. However, default methods
72 * are used in subsequent revisions of the {@code javax.lang.model.*}
73 * packages that are only required to run on Java SE 8 and higher
74 * platform versions.
75 *
76 * @param <R> the return type of this visitor's methods
77 * @param <P> the type of the additional parameter to this visitor's methods.
78 * @author Joseph D. Darcy
79 * @author Scott Seligman
80 * @author Peter von der Ahé
81 * @since 1.6
82 */
83 public interface AnnotationValueVisitor<R, P> {
84 /**
85 * Visits an annotation value.
86 * @param av the value to visit
87 * @param p a visitor-specified parameter
88 * @return a visitor-specified result
89 */
90 R visit(AnnotationValue av, P p);
91
92 /**
93 * A convenience method equivalent to {@code visit(av, null)}.
94 *
95 * @implSpec The default implementation is {@code visit(av, null)}.
96 *
97 * @param av the value to visit
98 * @return a visitor-specified result
99 */
100 default R visit(AnnotationValue av) {
101 return visit(av, null);
102 }
103
104 /**
105 * Visits a {@code boolean} value in an annotation.
106 * @param b the value being visited
107 * @param p a visitor-specified parameter
108 * @return the result of the visit
109 */
110 R visitBoolean(boolean b, P p);
111
112 /**
113 * Visits a {@code byte} value in an annotation.
114 * @param b the value being visited
115 * @param p a visitor-specified parameter
116 * @return the result of the visit
117 */
118 R visitByte(byte b, P p);
119
120 /**
121 * Visits a {@code char} value in an annotation.
122 * @param c the value being visited
123 * @param p a visitor-specified parameter
124 * @return the result of the visit
125 */
126 R visitChar(char c, P p);
127
128 /**
129 * Visits a {@code double} value in an annotation.
130 * @param d the value being visited
131 * @param p a visitor-specified parameter
132 * @return the result of the visit
133 */
134 R visitDouble(double d, P p);
135
136 /**
137 * Visits a {@code float} value in an annotation.
138 * @param f the value being visited
139 * @param p a visitor-specified parameter
140 * @return the result of the visit
141 */
142 R visitFloat(float f, P p);
143
144 /**
145 * Visits an {@code int} value in an annotation.
146 * @param i the value being visited
147 * @param p a visitor-specified parameter
148 * @return the result of the visit
149 */
150 R visitInt(int i, P p);
151
152 /**
153 * Visits a {@code long} value in an annotation.
154 * @param i the value being visited
155 * @param p a visitor-specified parameter
156 * @return the result of the visit
157 */
158 R visitLong(long i, P p);
159
160 /**
161 * Visits a {@code short} value in an annotation.
162 * @param s the value being visited
163 * @param p a visitor-specified parameter
164 * @return the result of the visit
165 */
166 R visitShort(short s, P p);
167
168 /**
169 * Visits a string value in an annotation.
170 * @param s the value being visited
171 * @param p a visitor-specified parameter
172 * @return the result of the visit
173 */
174 R visitString(String s, P p);
175
176 /**
177 * Visits a type value in an annotation.
178 * @param t the value being visited
179 * @param p a visitor-specified parameter
180 * @return the result of the visit
181 */
182 R visitType(TypeMirror t, P p);
183
184 /**
185 * Visits an {@code enum} value in an annotation.
186 * @param c the value being visited
187 * @param p a visitor-specified parameter
188 * @return the result of the visit
189 */
190 R visitEnumConstant(VariableElement c, P p);
191
192 /**
193 * Visits an annotation value in an annotation.
194 * @param a the value being visited
195 * @param p a visitor-specified parameter
196 * @return the result of the visit
197 */
198 R visitAnnotation(AnnotationMirror a, P p);
199
200 /**
201 * Visits an array value in an annotation.
202 * @param vals the value being visited
203 * @param p a visitor-specified parameter
204 * @return the result of the visit
205 */
206 R visitArray(List<? extends AnnotationValue> vals, P p);
207
208 /**
209 * Visits an unknown kind of annotation value.
210 * This can occur if the language evolves and new kinds
211 * of value can be stored in an annotation.
212 * @param av the unknown value being visited
213 * @param p a visitor-specified parameter
214 * @return the result of the visit
215 * @throws UnknownAnnotationValueException
216 * a visitor implementation may optionally throw this exception
217 */
218 R visitUnknown(AnnotationValue av, P p);
219 }