1 /*
2 * Copyright (c) 2011, 2018, 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 source versions {@link SourceVersion#RELEASE_9
37 * RELEASE_9} through {@link SourceVersion#RELEASE_12 RELEASE_12}.
38 *
39 * The <code>visit<i>Xyz</i></code> methods in this
40 * class scan their component elements by calling {@code scan} on
41 * their {@linkplain Element#getEnclosedElements enclosed elements},
42 * {@linkplain ExecutableElement#getParameters parameters}, etc., as
43 * indicated in the individual method specifications. A subclass can
44 * control the order elements are visited by overriding the
45 * <code>visit<i>Xyz</i></code> methods. Note that clients of a scanner
46 * may get the desired behavior be invoking {@code v.scan(e, p)} rather
47 * than {@code v.visit(e, p)} on the root objects of interest.
48 *
49 * <p>When a subclass overrides a <code>visit<i>Xyz</i></code> method, the
50 * new method can cause the enclosed elements to be scanned in the
51 * default way by calling <code>super.visit<i>Xyz</i></code>. In this
52 * fashion, the concrete visitor can control the ordering of traversal
53 * over the component elements with respect to the additional
54 * processing; for example, consistently calling
55 * <code>super.visit<i>Xyz</i></code> at the start of the overridden
56 * methods will yield a preorder traversal, etc. If the component
57 * elements should be traversed in some other order, instead of
58 * calling <code>super.visit<i>Xyz</i></code>, an overriding visit method
59 * should call {@code scan} with the elements in the desired order.
60 *
61 * <p> Methods in this class may be overridden subject to their
62 * general contract. Note that annotating methods in concrete
63 * subclasses with {@link java.lang.Override @Override} will help
64 * ensure that methods are overridden as intended.
65 *
66 * <p> <b>WARNING:</b> The {@code ElementVisitor} interface
67 * implemented by this class may have methods added to it in the
68 * future to accommodate new, currently unknown, language structures
69 * added to future versions of the Java™ programming language.
70 * Therefore, methods whose names begin with {@code "visit"} may be
71 * added to this class in the future; to avoid incompatibilities,
72 * classes which extend this class should not declare any instance
73 * methods with names beginning with {@code "visit"}.
74 *
75 * <p>When such a new visit method is added, the default
76 * implementation in this class will be to call the {@link
77 * #visitUnknown visitUnknown} method. A new element scanner visitor
78 * class will also be introduced to correspond to the new language
79 * level; this visitor will have different default behavior for the
80 * visit method in question. When the new visitor is introduced, all
81 * or portions of this visitor may be deprecated.
82 *
83 * @param <R> the return type of this visitor's methods. Use {@link
84 * Void} for visitors that do not need to return results.
85 * @param <P> the type of the additional parameter to this visitor's
86 * methods. Use {@code Void} for visitors that do not need an
87 * additional parameter.
88 *
89 * @see ElementScanner6
90 * @see ElementScanner7
91 * @see ElementScanner8
92 * @since 9
93 * @spec JPMS
94 */
95 @SupportedSourceVersion(RELEASE_12)
96 public class ElementScanner9<R, P> extends ElementScanner8<R, P> {
97 /**
98 * Constructor for concrete subclasses; uses {@code null} for the
99 * default value.
100 */
101 protected ElementScanner9(){
102 super(null);
103 }
104
105 /**
106 * Constructor for concrete subclasses; uses the argument for the
107 * default value.
108 *
109 * @param defaultValue the default value
110 */
111 protected ElementScanner9(R defaultValue){
112 super(defaultValue);
113 }
114
115 /**
116 * {@inheritDoc}
117 *
118 * @implSpec This implementation scans the enclosed elements.
119 *
120 * @param e the element to visit
121 * @param p a visitor-specified parameter
122 * @return the result of the scan
123 */
124 @Override
125 public R visitModule(ModuleElement e, P p) {
126 return scan(e.getEnclosedElements(), p); // TODO: Hmmm, this might not be right
127 }
128 }