1 /*
2 * Copyright (c) 2005, 2019, 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 * <p> Methods in this class may be overridden subject to their
60 * general contract. Note that annotating methods in concrete
61 * subclasses with {@link java.lang.Override @Override} will help
62 * ensure that methods are overridden as intended.
63 *
64 * <p> <b>WARNING:</b> The {@code ElementVisitor} interface
65 * implemented by this class may have methods added to it in the
66 * future to accommodate new, currently unknown, language structures
67 * added to future versions of the Java™ programming language.
68 * Therefore, methods whose names begin with {@code "visit"} may be
69 * added to this class in the future; to avoid incompatibilities,
70 * classes which extend this class should not declare any instance
71 * methods with names beginning with {@code "visit"}.
72 *
73 * <p>When such a new visit method is added, the default
74 * implementation in this class will be to call the {@link
75 * #visitUnknown visitUnknown} method. A new element scanner visitor
76 * class will also be introduced to correspond to the new language
77 * level; this visitor will have different default behavior for the
78 * visit method in question. When the new visitor is introduced, all
79 * or portions of this visitor may be deprecated.
80 *
81 * @param <R> the return type of this visitor's methods. Use {@link
82 * Void} for visitors that do not need to return results.
83 * @param <P> the type of the additional parameter to this visitor's
84 * methods. Use {@code Void} for visitors that do not need an
85 * additional parameter.
86 *
87 * @author Joseph D. Darcy
88 * @author Scott Seligman
89 * @author Peter von der Ahé
90 *
91 * @see ElementScanner7
92 * @see ElementScanner8
93 * @see ElementScanner9
94 * @see ElementScanner14
95 * @since 1.6
96 */
97 @SupportedSourceVersion(RELEASE_6)
98 public class ElementScanner6<R, P> extends AbstractElementVisitor6<R, P> {
99 /**
100 * The specified default value.
101 */
102 protected final R DEFAULT_VALUE;
103
104 /**
105 * Constructor for concrete subclasses; uses {@code null} for the
106 * default value.
107 * @deprecated Release 6 is obsolete; update to a visitor for a newer
108 * release level.
109 */
110 @Deprecated(since="9")
111 protected ElementScanner6(){
112 DEFAULT_VALUE = null;
113 }
114
115 /**
116 * Constructor for concrete subclasses; uses the argument for the
117 * default value.
118 *
119 * @param defaultValue the default value
120 * @deprecated Release 6 is obsolete; update to a visitor for a newer
121 * release level.
122 */
123 @Deprecated(since="9")
124 protected ElementScanner6(R defaultValue){
125 DEFAULT_VALUE = defaultValue;
126 }
127
128 /**
129 * Iterates over the given elements and calls {@link
130 * #scan(Element, Object) scan(Element, P)} on each one. Returns
131 * the result of the last call to {@code scan} or {@code
132 * DEFAULT_VALUE} for an empty iterable.
133 *
134 * @param iterable the elements to scan
135 * @param p additional parameter
136 * @return the scan of the last element or {@code DEFAULT_VALUE} if no elements
137 */
138 public final R scan(Iterable<? extends Element> iterable, P p) {
139 R result = DEFAULT_VALUE;
140 for(Element e : iterable)
141 result = scan(e, p);
142 return result;
143 }
144
145 /**
146 * Processes an element by calling {@code e.accept(this, p)};
147 * this method may be overridden by subclasses.
148 *
149 * @param e the element to scan
150 * @param p a scanner-specified parameter
151 * @return the result of visiting {@code e}.
152 */
153 public R scan(Element e, P p) {
154 return e.accept(this, p);
155 }
156
157 /**
158 * Convenience method equivalent to {@code v.scan(e, null)}.
159 *
160 * @param e the element to scan
161 * @return the result of scanning {@code e}.
162 */
163 public final R scan(Element e) {
164 return scan(e, null);
165 }
166
167 /**
168 * {@inheritDoc}
169 *
170 * @implSpec This implementation scans the enclosed elements.
171 *
172 * @param e {@inheritDoc}
173 * @param p {@inheritDoc}
174 * @return the result of scanning
175 */
176 public R visitPackage(PackageElement e, P p) {
177 return scan(e.getEnclosedElements(), p);
178 }
179
180 /**
181 * {@inheritDoc}
182 *
183 * @implSpec This implementation scans the enclosed elements.
184 * Note that type parameters are <em>not</em> scanned by this
185 * implementation since type parameters are not considered to be
186 * {@linkplain TypeElement#getEnclosedElements enclosed elements
187 * of a type}.
188 *
189 * @param e {@inheritDoc}
190 * @param p {@inheritDoc}
191 * @return the result of scanning
192 */
193 public R visitType(TypeElement e, P p) {
194 return scan(e.getEnclosedElements(), p);
195 }
196
197 /**
198 * {@inheritDoc}
199 *
200 * @implSpec This implementation scans the enclosed elements, unless the
201 * element is a {@code RESOURCE_VARIABLE} in which case {@code
202 * visitUnknown} is called.
203 *
204 * @param e {@inheritDoc}
205 * @param p {@inheritDoc}
206 * @return the result of scanning
207 */
208 public R visitVariable(VariableElement e, P p) {
209 if (e.getKind() != ElementKind.RESOURCE_VARIABLE)
210 return scan(e.getEnclosedElements(), p);
211 else
212 return visitUnknown(e, p);
213 }
214
215 /**
216 * {@inheritDoc}
217 *
218 * @implSpec This implementation scans the parameters.
219 * Note that type parameters are <em>not</em> scanned by this
220 * implementation.
221 *
222 * @param e {@inheritDoc}
223 * @param p {@inheritDoc}
224 * @return the result of scanning
225 */
226 public R visitExecutable(ExecutableElement e, P p) {
227 return scan(e.getParameters(), p);
228 }
229
230 /**
231 * {@inheritDoc}
232 *
233 * @implSpec This implementation scans the enclosed elements.
234 *
235 * @param e {@inheritDoc}
236 * @param p {@inheritDoc}
237 * @return the result of scanning
238 */
239 public R visitTypeParameter(TypeParameterElement e, P p) {
240 return scan(e.getEnclosedElements(), p);
241 }
242 }