1 /*
2 * Copyright (c) 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 java.util.List;
29 import java.util.ArrayList;
30 import javax.lang.model.element.*;
31 import javax.annotation.processing.SupportedSourceVersion;
32 import javax.lang.model.SourceVersion;
33 import static javax.lang.model.SourceVersion.*;
34
35 /**
36 * {@preview Associated with records, a preview feature of the Java language.
37 *
38 * This class is associated with <i>records</i>, a preview
39 * feature of the Java language. Preview features
40 * may be removed in a future release, or upgraded to permanent
41 * features of the Java language.}
42 *
43 * A scanning visitor of program elements with default behavior
44 * appropriate for the {@link SourceVersion#RELEASE_14 RELEASE_14}
45 * source version.
46 *
47 * The <code>visit<i>Xyz</i></code> methods in this
48 * class scan their component elements by calling {@code scan} on
49 * their {@linkplain Element#getEnclosedElements enclosed elements},
50 * {@linkplain ExecutableElement#getParameters parameters}, etc., as
51 * indicated in the individual method specifications. A subclass can
52 * control the order elements are visited by overriding the
53 * <code>visit<i>Xyz</i></code> methods. Note that clients of a scanner
54 * may get the desired behavior be invoking {@code v.scan(e, p)} rather
55 * than {@code v.visit(e, p)} on the root objects of interest.
56 *
57 * <p>When a subclass overrides a <code>visit<i>Xyz</i></code> method, the
58 * new method can cause the enclosed elements to be scanned in the
59 * default way by calling <code>super.visit<i>Xyz</i></code>. In this
60 * fashion, the concrete visitor can control the ordering of traversal
61 * over the component elements with respect to the additional
62 * processing; for example, consistently calling
63 * <code>super.visit<i>Xyz</i></code> at the start of the overridden
64 * methods will yield a preorder traversal, etc. If the component
65 * elements should be traversed in some other order, instead of
66 * calling <code>super.visit<i>Xyz</i></code>, an overriding visit method
67 * should call {@code scan} with the elements in the desired order.
68 *
69 * <p> Methods in this class may be overridden subject to their
70 * general contract. Note that annotating methods in concrete
71 * subclasses with {@link java.lang.Override @Override} will help
72 * ensure that methods are overridden as intended.
73 *
74 * <p> <b>WARNING:</b> The {@code ElementVisitor} interface
75 * implemented by this class may have methods added to it in the
76 * future to accommodate new, currently unknown, language structures
77 * added to future versions of the Java™ programming language.
78 * Therefore, methods whose names begin with {@code "visit"} may be
79 * added to this class in the future; to avoid incompatibilities,
80 * classes which extend this class should not declare any instance
81 * methods with names beginning with {@code "visit"}.
82 *
83 * <p>When such a new visit method is added, the default
84 * implementation in this class will be to call the {@link
85 * #visitUnknown visitUnknown} method. A new element scanner visitor
86 * class will also be introduced to correspond to the new language
87 * level; this visitor will have different default behavior for the
88 * visit method in question. When the new visitor is introduced, all
89 * or portions of this visitor may be deprecated.
90 *
91 * @param <R> the return type of this visitor's methods. Use {@link
92 * Void} for visitors that do not need to return results.
93 * @param <P> the type of the additional parameter to this visitor's
94 * methods. Use {@code Void} for visitors that do not need an
95 * additional parameter.
96 *
97 * @see ElementScanner6
98 * @see ElementScanner7
99 * @see ElementScanner8
100 * @see ElementScanner9
101 * @since 14
102 */
103 @jdk.internal.PreviewFeature(feature=jdk.internal.PreviewFeature.Feature.RECORDS,
104 essentialAPI=false)
105 @SupportedSourceVersion(RELEASE_14)
106 public class ElementScanner14<R, P> extends ElementScanner9<R, P> {
107 /**
108 * Constructor for concrete subclasses; uses {@code null} for the
109 * default value.
110 */
111 protected ElementScanner14(){
112 super(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 */
121 protected ElementScanner14(R defaultValue){
122 super(defaultValue);
123 }
124
125 /**
126 * {@inheritDoc}
127 *
128 * @implSpec This implementation scans the type parameters, if
129 * any, and then the enclosed elements.
130 *
131 *
132 * @param e {@inheritDoc}
133 * @param p {@inheritDoc}
134 * @return the result of scanning
135 */
136 @Override
137 public R visitType(TypeElement e, P p) {
138 return scan(createScanningList(e, e.getEnclosedElements()), p);
139 }
140
141 /**
142 * {@inheritDoc}
143 *
144 * @implSpec This implementation first scans the type parameters, if any, and then
145 * the parameters.
146 *
147 * @param e {@inheritDoc}
148 * @param p {@inheritDoc}
149 * @return the result of scanning
150 */
151 public R visitExecutable(ExecutableElement e, P p) {
152 return scan(createScanningList(e, e.getParameters()), p);
153 }
154
155 private List<? extends Element> createScanningList(Parameterizable element,
156 List<? extends Element> toBeScanned) {
157 var typeParameters = element.getTypeParameters();
158 if (typeParameters.isEmpty()) {
159 return toBeScanned;
160 } else {
161 List<Element> scanningList = new ArrayList<>(typeParameters);
162 scanningList.addAll(toBeScanned);
163 return scanningList;
164 }
165 }
166
167 /**
168 * {@inheritDoc}
169 *
170 * @implSpec This implementation scans the enclosed elements.
171 *
172 * @param e the element to visit
173 * @param p a visitor-specified parameter
174 * @return the result of the scan
175 */
176 @SuppressWarnings("preview")
177 @Override
178 public R visitRecordComponent(RecordComponentElement e, P p) {
179 return scan(e.getEnclosedElements(), p);
180 }
181 }