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.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 scanning visitor of program elements with default behavior
36 * appropriate for the {@link SourceVersion#RELEASE_6 RELEASE_6}
37 * source version. The <code>visit<i>Xyz</i></code> methods in this
38 * class scan their component elements by calling {@code scan} on
39 * their {@linkplain Element#getEnclosedElements enclosed elements},
40 * {@linkplain ExecutableElement#getParameters parameters}, etc., as
41 * indicated in the individual method specifications. A subclass can
42 * control the order elements are visited by overriding the
43 * <code>visit<i>Xyz</i></code> methods. Note that clients of a scanner
44 * may get the desired behavior be invoking {@code v.scan(e, p)} rather
45 * than {@code v.visit(e, p)} on the root objects of interest.
46 *
47 * <p>When a subclass overrides a <code>visit<i>Xyz</i></code> method, the
48 * new method can cause the enclosed elements to be scanned in the
49 * default way by calling <code>super.visit<i>Xyz</i></code>. In this
50 * fashion, the concrete visitor can control the ordering of traversal
51 * over the component elements with respect to the additional
52 * processing; for example, consistently calling
53 * <code>super.visit<i>Xyz</i></code> at the start of the overridden
54 * methods will yield a preorder traversal, etc. If the component
55 * elements should be traversed in some other order, instead of
56 * calling <code>super.visit<i>Xyz</i></code>, an overriding visit method
57 * should call {@code scan} with the elements in the desired order.
58 *
59 * @apiNote
60 * Methods in this class may be overridden subject to their general
61 * contract.
62 *
63 * <p id=note_for_subclasses><strong>WARNING:</strong> The {@code ElementVisitor} interface
64 * implemented by this class may have methods added to it in the
65 * future to accommodate new, currently unknown, language structures
66 * added to future versions of the Java programming language.
67 * Therefore, methods whose names begin with {@code "visit"} may be
68 * added to this class in the future; to avoid incompatibilities,
69 * classes which extend this class should not declare any instance
70 * methods with names beginning with {@code "visit"}.</p>
71 *
72 * <p>When such a new visit method is added, the default
73 * implementation in this class will be to directly or indirectly call the {@link
74 * #visitUnknown visitUnknown} method. A new element scanner visitor
75 * class will also be introduced to correspond to the new language
76 * level; this visitor will have different default behavior for the
77 * visit method in question. When a new visitor is introduced,
78 * portions of this visitor class may be deprecated, including its constructors.
79 *
80 * @param <R> the return type of this visitor's methods. Use {@link
81 * Void} for visitors that do not need to return results.
82 * @param <P> the type of the additional parameter to this visitor's
83 * methods. Use {@code Void} for visitors that do not need an
84 * additional parameter.
85 *
86 * @author Joseph D. Darcy
87 * @author Scott Seligman
88 * @author Peter von der Ahé
89 *
90 * @see ElementScanner7
91 * @see ElementScanner8
92 * @see ElementScanner9
93 * @see ElementScanner14
94 * @since 1.6
95 */
96 @SupportedSourceVersion(RELEASE_6)
97 public class ElementScanner6<R, P> extends AbstractElementVisitor6<R, P> {
98 /**
99 * The specified default value.
100 */
101 protected final R DEFAULT_VALUE;
102
103 /**
104 * Constructor for concrete subclasses; uses {@code null} for the
105 * default value.
106 * @deprecated Release 6 is obsolete; update to a visitor for a newer
107 * release level.
108 */
109 @Deprecated(since="9")
110 protected ElementScanner6(){
111 DEFAULT_VALUE = null;
112 }
113
114 /**
115 * Constructor for concrete subclasses; uses the argument for the
116 * default value.
117 *
118 * @param defaultValue the default value
119 * @deprecated Release 6 is obsolete; update to a visitor for a newer
120 * release level.
121 */
122 @Deprecated(since="9")
123 protected ElementScanner6(R defaultValue){
124 DEFAULT_VALUE = defaultValue;
125 }
126
127 /**
128 * Iterates over the given elements and calls {@link
129 * #scan(Element, Object) scan(Element, P)} on each one. Returns
130 * the result of the last call to {@code scan} or {@code
131 * DEFAULT_VALUE} for an empty iterable.
132 *
133 * @param iterable the elements to scan
134 * @param p additional parameter
135 * @return the scan of the last element or {@code DEFAULT_VALUE} if no elements
136 */
137 public final R scan(Iterable<? extends Element> iterable, P p) {
138 R result = DEFAULT_VALUE;
139 for(Element e : iterable)
140 result = scan(e, p);
141 return result;
142 }
143
144 /**
145 * Processes an element by calling {@code e.accept(this, p)};
146 * this method may be overridden by subclasses.
147 *
148 * @param e the element to scan
149 * @param p a scanner-specified parameter
150 * @return the result of visiting {@code e}.
151 */
152 public R scan(Element e, P p) {
153 return e.accept(this, p);
154 }
155
156 /**
157 * Convenience method equivalent to {@code v.scan(e, null)}.
158 *
159 * @param e the element to scan
160 * @return the result of scanning {@code e}.
161 */
162 public final R scan(Element e) {
163 return scan(e, null);
164 }
165
166 /**
167 * {@inheritDoc}
168 *
169 * @implSpec This implementation scans the enclosed elements.
170 *
171 * @param e {@inheritDoc}
172 * @param p {@inheritDoc}
173 * @return the result of scanning
174 */
175 public R visitPackage(PackageElement e, P p) {
176 return scan(e.getEnclosedElements(), p);
177 }
178
179 /**
180 * {@inheritDoc}
181 *
182 * @implSpec This implementation scans the enclosed elements.
183 * Note that type parameters are <em>not</em> scanned by this
184 * implementation since type parameters are not considered to be
185 * {@linkplain TypeElement#getEnclosedElements enclosed elements
186 * of a type}.
187 *
188 * @param e {@inheritDoc}
189 * @param p {@inheritDoc}
190 * @return the result of scanning
191 */
192 public R visitType(TypeElement e, P p) {
193 return scan(e.getEnclosedElements(), p);
194 }
195
196 /**
197 * {@inheritDoc}
198 *
199 * @implSpec This implementation scans the enclosed elements, unless the
200 * element is a {@code RESOURCE_VARIABLE} in which case {@code
201 * visitUnknown} is called.
202 *
203 * @param e {@inheritDoc}
204 * @param p {@inheritDoc}
205 * @return the result of scanning
206 */
207 public R visitVariable(VariableElement e, P p) {
208 if (e.getKind() != ElementKind.RESOURCE_VARIABLE)
209 return scan(e.getEnclosedElements(), p);
210 else
211 return visitUnknown(e, p);
212 }
213
214 /**
215 * {@inheritDoc}
216 *
217 * @implSpec This implementation scans the parameters.
218 * Note that type parameters are <em>not</em> scanned by this
219 * implementation.
220 *
221 * @param e {@inheritDoc}
222 * @param p {@inheritDoc}
223 * @return the result of scanning
224 */
225 public R visitExecutable(ExecutableElement e, P p) {
226 return scan(e.getParameters(), p);
227 }
228
229 /**
230 * {@inheritDoc}
231 *
232 * @implSpec This implementation scans the enclosed elements.
233 *
234 * @param e {@inheritDoc}
235 * @param p {@inheritDoc}
236 * @return the result of scanning
237 */
238 public R visitTypeParameter(TypeParameterElement e, P p) {
239 return scan(e.getEnclosedElements(), p);
240 }
241 }