1 /*
2 * Copyright (c) 2005, 2013, 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.util;
27
28 import javax.lang.model.element.*;
29 import javax.annotation.processing.SupportedSourceVersion;
30 import javax.lang.model.SourceVersion;
31 import static javax.lang.model.SourceVersion.*;
32
33
34 /**
35 * A simple visitor of program elements with default behavior
36 * appropriate for the {@link SourceVersion#RELEASE_6 RELEASE_6}
37 * source version.
38 *
39 * Visit methods corresponding to {@code RELEASE_6} language
40 * constructs call {@link #defaultAction defaultAction}, passing their
41 * arguments to {@code defaultAction}'s corresponding parameters.
42 *
43 * For constructs introduced in {@code RELEASE_7} and later, {@code
44 * visitUnknown} is called instead.
45 *
46 * <p> Methods in this class may be overridden subject to their
47 * general contract. Note that annotating methods in concrete
48 * subclasses with {@link java.lang.Override @Override} will help
49 * ensure that methods are overridden as intended.
50 *
51 * <p> <b>WARNING:</b> The {@code ElementVisitor} interface
52 * implemented by this class may have methods added to it in the
53 * future to accommodate new, currently unknown, language structures
54 * added to future versions of the Java™ programming language.
55 * Therefore, methods whose names begin with {@code "visit"} may be
56 * added to this class in the future; to avoid incompatibilities,
57 * classes which extend this class should not declare any instance
58 * methods with names beginning with {@code "visit"}.
59 *
60 * <p>When such a new visit method is added, the default
61 * implementation in this class will be to call the {@link
62 * #visitUnknown visitUnknown} method. A new simple element visitor
63 * class will also be introduced to correspond to the new language
64 * level; this visitor will have different default behavior for the
65 * visit method in question. When the new visitor is introduced, all
66 * or portions of this visitor may be deprecated.
67 *
68 * <p>Note that adding a default implementation of a new visit method
69 * in a visitor class will occur instead of adding a <em>default
70 * method</em> directly in the visitor interface since a Java SE 8
71 * language feature cannot be used to this version of the API since
72 * this version is required to be runnable on Java SE 7
73 * implementations. Future versions of the API that are only required
74 * to run on Java SE 8 and later may take advantage of default methods
75 * in this situation.
76 *
77 * @param <R> the return type of this visitor's methods. Use {@code Void}
78 * for visitors that do not need to return results.
79 * @param <P> the type of the additional parameter to this visitor's methods. Use {@code Void}
80 * for visitors that do not need an additional parameter.
81 *
82 * @author Joseph D. Darcy
83 * @author Scott Seligman
84 * @author Peter von der Ahé
85 *
86 * @see SimpleElementVisitor7
87 * @see SimpleElementVisitor8
88 * @since 1.6
89 */
90 @SupportedSourceVersion(RELEASE_6)
91 public class SimpleElementVisitor6<R, P> extends AbstractElementVisitor6<R, P> {
92 /**
93 * Default value to be returned; {@link #defaultAction
94 * defaultAction} returns this value unless the method is
95 * overridden.
96 */
97 protected final R DEFAULT_VALUE;
98
99 /**
100 * Constructor for concrete subclasses; uses {@code null} for the
101 * default value.
102 */
103 protected SimpleElementVisitor6(){
104 DEFAULT_VALUE = null;
105 }
106
107 /**
108 * Constructor for concrete subclasses; uses the argument for the
109 * default value.
110 *
111 * @param defaultValue the value to assign to {@link #DEFAULT_VALUE}
112 */
113 protected SimpleElementVisitor6(R defaultValue){
114 DEFAULT_VALUE = defaultValue;
115 }
116 /**
117 * The default action for visit methods. The implementation in
118 * this class just returns {@link #DEFAULT_VALUE}; subclasses will
119 * commonly override this method.
120 *
121 * @param e the element to process
122 * @param p a visitor-specified parameter
123 * @return {@code DEFAULT_VALUE} unless overridden
124 */
125 protected R defaultAction(Element e, P p) {
126 return DEFAULT_VALUE;
127 }
128
129 /**
130 * {@inheritDoc} This implementation calls {@code defaultAction}.
131 *
132 * @param e {@inheritDoc}
133 * @param p {@inheritDoc}
134 * @return the result of {@code defaultAction}
135 */
136 public R visitPackage(PackageElement e, P p) {
137 return defaultAction(e, p);
138 }
139
140 /**
141 * {@inheritDoc} This implementation calls {@code defaultAction}.
142 *
143 * @param e {@inheritDoc}
144 * @param p {@inheritDoc}
145 * @return the result of {@code defaultAction}
146 */
147 public R visitType(TypeElement e, P p) {
148 return defaultAction(e, p);
149 }
150
151 /**
152 * {@inheritDoc}
153 *
154 * This implementation calls {@code defaultAction}, unless the
155 * element is a {@code RESOURCE_VARIABLE} in which case {@code
156 * visitUnknown} is called.
157 *
158 * @param e {@inheritDoc}
159 * @param p {@inheritDoc}
160 * @return the result of {@code defaultAction} or {@code visitUnknown}
161 */
162 public R visitVariable(VariableElement e, P p) {
163 if (e.getKind() != ElementKind.RESOURCE_VARIABLE)
164 return defaultAction(e, p);
165 else
166 return visitUnknown(e, p);
167 }
168
169 /**
170 * {@inheritDoc} This implementation calls {@code defaultAction}.
171 *
172 * @param e {@inheritDoc}
173 * @param p {@inheritDoc}
174 * @return the result of {@code defaultAction}
175 */
176 public R visitExecutable(ExecutableElement e, P p) {
177 return defaultAction(e, p);
178 }
179
180 /**
181 * {@inheritDoc} This implementation calls {@code defaultAction}.
182 *
183 * @param e {@inheritDoc}
184 * @param p {@inheritDoc}
185 * @return the result of {@code defaultAction}
186 */
187 public R visitTypeParameter(TypeParameterElement e, P p) {
188 return defaultAction(e, p);
189 }
190 }