001 /*
002 * Copyright 2005-2006 Sun Microsystems, Inc. All Rights Reserved.
003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004 *
005 * This code is free software; you can redistribute it and/or modify it
006 * under the terms of the GNU General Public License version 2 only, as
007 * published by the Free Software Foundation. Sun designates this
008 * particular file as subject to the "Classpath" exception as provided
009 * by Sun in the LICENSE file that accompanied this code.
010 *
011 * This code is distributed in the hope that it will be useful, but WITHOUT
012 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014 * version 2 for more details (a copy is included in the LICENSE file that
015 * accompanied this code).
016 *
017 * You should have received a copy of the GNU General Public License version
018 * 2 along with this work; if not, write to the Free Software Foundation,
019 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020 *
021 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022 * CA 95054 USA or visit www.sun.com if you need additional information or
023 * have any questions.
024 */
025
026 package javax.lang.model.element;
027
028 import javax.lang.model.util.*;
029
030 /**
031 * A visitor of program elements, in the style of the visitor design
032 * pattern. Classes implementing this interface are used to operate
033 * on an element when the kind of element is unknown at compile time.
034 * When a visitor is passed to an element's {@link Element#accept
035 * accept} method, the <tt>visit<i>XYZ</i></tt> method most applicable
036 * to that element is invoked.
037 *
038 * <p> Classes implementing this interface may or may not throw a
039 * {@code NullPointerException} if the additional parameter {@code p}
040 * is {@code null}; see documentation of the implementing class for
041 * details.
042 *
043 * <p> <b>WARNING:</b> It is possible that methods will be added to
044 * this interface to accommodate new, currently unknown, language
045 * structures added to future versions of the Java™ programming
046 * language. Therefore, visitor classes directly implementing this
047 * interface may be source incompatible with future versions of the
048 * platform. To avoid this source incompatibility, visitor
049 * implementations are encouraged to instead extend the appropriate
050 * abstract visitor class that implements this interface. However, an
051 * API should generally use this visitor interface as the type for
052 * parameters, return type, etc. rather than one of the abstract
053 * classes.
054 *
055 * @param <R> the return type of this visitor's methods. Use {@link
056 * Void} for visitors that do not need to return results.
057 * @param <P> the type of the additional parameter to this visitor's
058 * methods. Use {@code Void} for visitors that do not need an
059 * additional parameter.
060 *
061 * @author Joseph D. Darcy
062 * @author Scott Seligman
063 * @author Peter von der Ahé
064 * @version 1.10 07/05/05
065 * @see AbstractElementVisitor6
066 * @since 1.6
067 */
068 public interface ElementVisitor<R, P> {
069 /**
070 * Visits an element.
071 * @param e the element to visit
072 * @param p a visitor-specified parameter
073 * @return a visitor-specified result
074 */
075 R visit(Element e, P p);
076
077 /**
078 * A convenience method equivalent to {@code v.visit(e, null)}.
079 * @param e the element to visit
080 * @return a visitor-specified result
081 */
082 R visit(Element e);
083
084 /**
085 * Visits a package element.
086 * @param e the element to visit
087 * @param p a visitor-specified parameter
088 * @return a visitor-specified result
089 */
090 R visitPackage(PackageElement e, P p);
091
092 /**
093 * Visits a type element.
094 * @param e the element to visit
095 * @param p a visitor-specified parameter
096 * @return a visitor-specified result
097 */
098 R visitType(TypeElement e, P p);
099
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 }
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