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.util;
027
028 import javax.lang.model.element.*;
029 import javax.annotation.processing.SupportedSourceVersion;
030 import static javax.lang.model.element.ElementKind.*;
031 import javax.lang.model.SourceVersion;
032 import static javax.lang.model.SourceVersion.*;
033
034
035 /**
036 * A scanning visitor of program elements with default behavior
037 * appropriate for the {@link SourceVersion#RELEASE_6 RELEASE_6}
038 * source version. The <tt>visit<i>XYZ</i></tt> methods in this
039 * class scan their component elements by calling {@code scan} on
040 * their {@linkplain Element#getEnclosedElements enclosed elements},
041 * {@linkplain ExecutableElement#getParameters parameters}, etc., as
042 * indicated in the individual method specifications. A subclass can
043 * control the order elements are visited by overriding the
044 * <tt>visit<i>XYZ</i></tt> methods. Note that clients of a scanner
045 * may get the desired behavior be invoking {@code v.scan(e, p)} rather
046 * than {@code v.visit(e, p)} on the root objects of interest.
047 *
048 * <p>When a subclass overrides a <tt>visit<i>XYZ</i></tt> method, the
049 * new method can cause the enclosed elements to be scanned in the
050 * default way by calling <tt>super.visit<i>XYZ</i></tt>. In this
051 * fashion, the concrete visitor can control the ordering of traversal
052 * over the component elements with respect to the additional
053 * processing; for example, consistently calling
054 * <tt>super.visit<i>XYZ</i></tt> at the start of the overridden
055 * methods will yield a preorder traversal, etc. If the component
056 * elements should be traversed in some other order, instead of
057 * calling <tt>super.visit<i>XYZ</i></tt>, an overriding visit method
058 * should call {@code scan} with the elements in the desired order.
059 *
060 * <p> Methods in this class may be overridden subject to their
061 * general contract. Note that annotating methods in concrete
062 * subclasses with {@link java.lang.Override @Override} will help
063 * ensure that methods are overridden as intended.
064 *
065 * <p> <b>WARNING:</b> The {@code ElementVisitor} interface
066 * implemented by this class may have methods added to it in the
067 * future to accommodate new, currently unknown, language structures
068 * added to future versions of the Java™ programming language.
069 * Therefore, methods whose names begin with {@code "visit"} may be
070 * added to this class in the future; to avoid incompatibilities,
071 * classes which extend this class should not declare any instance
072 * methods with names beginning with {@code "visit"}.
073 *
074 * <p>When such a new visit method is added, the default
075 * implementation in this class will be to call the {@link
076 * #visitUnknown visitUnknown} method. A new element scanner visitor
077 * class will also be introduced to correspond to the new language
078 * level; this visitor will have different default behavior for the
079 * visit method in question. When the new visitor is introduced, all
080 * or portions of this visitor may be deprecated.
081 *
082 * @param <R> the return type of this visitor's methods. Use {@link
083 * Void} for visitors that do not need to return results.
084 * @param <P> the type of the additional parameter to this visitor's
085 * methods. Use {@code Void} for visitors that do not need an
086 * additional parameter.
087 *
088 * @author Joseph D. Darcy
089 * @author Scott Seligman
090 * @author Peter von der Ahé
091 * @since 1.6
092 */
093 @SupportedSourceVersion(RELEASE_6)
094 public class ElementScanner6<R, P> extends AbstractElementVisitor6<R, P> {
095 /**
096 * The specified default value.
097 */
098 protected final R DEFAULT_VALUE;
099
100 /**
101 * Constructor for concrete subclasses; uses {@code null} for the
102 * default value.
103 */
104 protected ElementScanner6(){
105 DEFAULT_VALUE = null;
106 }
107
108 /**
109 * Constructor for concrete subclasses; uses the argument for the
110 * default value.
111 */
112 protected ElementScanner6(R defaultValue){
113 DEFAULT_VALUE = defaultValue;
114 }
115
116 /**
117 * Iterates over the given elements and calls {@link
118 * #scan(Element, Object) scan(Element, P)} on each one. Returns
119 * the result of the last call to {@code scan} or {@code
120 * DEFAULT_VALUE} for an empty iterable.
121 *
122 * @param iterable the elements to scan
123 * @param p additional parameter
124 * @return the scan of the last element or {@code DEFAULT_VALUE} if no elements
125 */
126 public final R scan(Iterable<? extends Element> iterable, P p) {
127 R result = DEFAULT_VALUE;
128 for(Element e : iterable)
129 result = scan(e, p);
130 return result;
131 }
132
133 /**
134 * Processes an element by calling {@code e.accept(this, p)};
135 * this method may be overridden by subclasses.
136 * @return the result of visiting {@code e}.
137 */
138 public R scan(Element e, P p) {
139 return e.accept(this, p);
140 }
141
142 /**
143 * Convenience method equivalent to {@code v.scan(e, null)}.
144 * @return the result of scanning {@code e}.
145 */
146 public final R scan(Element e) {
147 return scan(e, null);
148 }
149
150 /**
151 * {@inheritDoc} This implementation scans the enclosed elements.
152 *
153 * @param e the element to visit
154 * @param p a visitor-specified parameter
155 * @return the result of scanning
156 */
157 public R visitPackage(PackageElement e, P p) {
158 return scan(e.getEnclosedElements(), p);
159 }
160
161 /**
162 * {@inheritDoc} This implementation scans the enclosed elements.
163 *
164 * @param e the element to visit
165 * @param p a visitor-specified parameter
166 * @return the result of scanning
167 */
168 public R visitType(TypeElement e, P p) {
169 return scan(e.getEnclosedElements(), p);
170 }
171
172 /**
173 * {@inheritDoc} This implementation scans the enclosed elements.
174 *
175 * @param e the element to visit
176 * @param p a visitor-specified parameter
177 * @return the result of scanning
178 */
179 public R visitVariable(VariableElement e, P p) {
180 return scan(e.getEnclosedElements(), p);
181 }
182
183 /**
184 * {@inheritDoc} This implementation scans the parameters.
185 *
186 * @param e the element to visit
187 * @param p a visitor-specified parameter
188 * @return the result of scanning
189 */
190 public R visitExecutable(ExecutableElement e, P p) {
191 return scan(e.getParameters(), p);
192 }
193
194 /**
195 * {@inheritDoc} This implementation scans the enclosed elements.
196 *
197 * @param e the element to visit
198 * @param p a visitor-specified parameter
199 * @return the result of scanning
200 */
201 public R visitTypeParameter(TypeParameterElement e, P p) {
202 return scan(e.getEnclosedElements(), p);
203 }
204 }