1 /*
2 * Copyright 2005-2006 Sun Microsystems, Inc. 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. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any questions.
24 */
25
26 package javax.lang.model.element;
27
28 import javax.lang.model.util.*;
29
30 /**
31 * A visitor of program elements, in the style of the visitor design
32 * pattern. Classes implementing this interface are used to operate
33 * on an element when the kind of element is unknown at compile time.
34 * When a visitor is passed to an element's {@link Element#accept
35 * accept} method, the <tt>visit<i>XYZ</i></tt> method most applicable
36 * to that element is invoked.
37 *
38 * <p> Classes implementing this interface may or may not throw a
39 * {@code NullPointerException} if the additional parameter {@code p}
40 * is {@code null}; see documentation of the implementing class for
41 * details.
42 *
43 * <p> <b>WARNING:</b> It is possible that methods will be added to
44 * this interface to accommodate new, currently unknown, language
45 * structures added to future versions of the Java™ programming
46 * language. Therefore, visitor classes directly implementing this
47 * interface may be source incompatible with future versions of the
48 * platform. To avoid this source incompatibility, visitor
49 * implementations are encouraged to instead extend the appropriate
50 * abstract visitor class that implements this interface. However, an
51 * API should generally use this visitor interface as the type for
52 * parameters, return type, etc. rather than one of the abstract
53 * classes.
54 *
55 * @param <R> the return type of this visitor's methods. Use {@link
56 * Void} for visitors that do not need to return results.
57 * @param <P> the type of the additional parameter to this visitor's
58 * methods. Use {@code Void} for visitors that do not need an
59 * additional parameter.
60 *
61 * @author Joseph D. Darcy
62 * @author Scott Seligman
63 * @author Peter von der Ahé
64 * @see AbstractElementVisitor6
65 * @see AbstractElementVisitor7
66 * @since 1.6
67 */
68 public interface ElementVisitor<R, P> {
69 /**
70 * Visits an element.
71 * @param e the element to visit
72 * @param p a visitor-specified parameter
73 * @return a visitor-specified result
74 */
75 R visit(Element e, P p);
76
77 /**
78 * A convenience method equivalent to {@code v.visit(e, null)}.
79 * @param e the element to visit
80 * @return a visitor-specified result
81 */
82 R visit(Element e);
83
84 /**
85 * Visits a package element.
86 * @param e the element to visit
87 * @param p a visitor-specified parameter
88 * @return a visitor-specified result
89 */
90 R visitPackage(PackageElement e, P p);
91
92 /**
93 * Visits a type element.
94 * @param e the element to visit
95 * @param p a visitor-specified parameter
96 * @return a visitor-specified result
97 */
98 R visitType(TypeElement e, P p);
99
100 /**
101 * Visits a variable element.
102 * @param e the element to visit
103 * @param p a visitor-specified parameter
104 * @return a visitor-specified result
105 */
106 R visitVariable(VariableElement e, P p);
107
108 /**
109 * Visits an executable element.
110 * @param e the element to visit
111 * @param p a visitor-specified parameter
112 * @return a visitor-specified result
113 */
114 R visitExecutable(ExecutableElement e, P p);
115
116 /**
117 * Visits a type parameter element.
118 * @param e the element to visit
119 * @param p a visitor-specified parameter
120 * @return a visitor-specified result
121 */
122 R visitTypeParameter(TypeParameterElement e, P p);
123
124 /**
125 * Visits an unknown kind of element.
126 * This can occur if the language evolves and new kinds
127 * of elements are added to the {@code Element} hierarchy.
128 *
129 * @param e the element to visit
130 * @param p a visitor-specified parameter
131 * @return a visitor-specified result
132 * @throws UnknownElementException
133 * a visitor implementation may optionally throw this exception
134 */
135 R visitUnknown(Element e, P p);
136 }