1 /* 2 * Copyright (c) 2005, 2011, 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 static javax.lang.model.element.ElementKind.*; 31 import javax.lang.model.SourceVersion; 32 import static javax.lang.model.SourceVersion.*; 33 34 35 /** 36 * A scanning visitor of program elements with default behavior 37 * appropriate for the {@link SourceVersion#RELEASE_6 RELEASE_6} 38 * source version. The <tt>visit<i>XYZ</i></tt> methods in this 39 * class scan their component elements by calling {@code scan} on 40 * their {@linkplain Element#getEnclosedElements enclosed elements}, 41 * {@linkplain ExecutableElement#getParameters parameters}, etc., as 42 * indicated in the individual method specifications. A subclass can 43 * control the order elements are visited by overriding the 44 * <tt>visit<i>XYZ</i></tt> methods. Note that clients of a scanner 45 * may get the desired behavior be invoking {@code v.scan(e, p)} rather 46 * than {@code v.visit(e, p)} on the root objects of interest. 47 * 48 * <p>When a subclass overrides a <tt>visit<i>XYZ</i></tt> method, the 49 * new method can cause the enclosed elements to be scanned in the 50 * default way by calling <tt>super.visit<i>XYZ</i></tt>. In this 51 * fashion, the concrete visitor can control the ordering of traversal 52 * over the component elements with respect to the additional 53 * processing; for example, consistently calling 54 * <tt>super.visit<i>XYZ</i></tt> at the start of the overridden 55 * methods will yield a preorder traversal, etc. If the component 56 * elements should be traversed in some other order, instead of 57 * calling <tt>super.visit<i>XYZ</i></tt>, an overriding visit method 58 * should call {@code scan} with the elements in the desired order. 59 * 60 * <p> Methods in this class may be overridden subject to their 61 * general contract. Note that annotating methods in concrete 62 * subclasses with {@link java.lang.Override @Override} will help 63 * ensure that methods are overridden as intended. 64 * 65 * <p> <b>WARNING:</b> The {@code ElementVisitor} interface 66 * implemented by this class may have methods added to it in the 67 * future to accommodate new, currently unknown, language structures 68 * added to future versions of the Java™ programming language. 69 * Therefore, methods whose names begin with {@code "visit"} may be 70 * added to this class in the future; to avoid incompatibilities, 71 * classes which extend this class should not declare any instance 72 * methods with names beginning with {@code "visit"}. 73 * 74 * <p>When such a new visit method is added, the default 75 * implementation in this class will be to call the {@link 76 * #visitUnknown visitUnknown} method. A new element scanner visitor 77 * class will also be introduced to correspond to the new language 78 * level; this visitor will have different default behavior for the 79 * visit method in question. When the new visitor is introduced, all 80 * or portions of this visitor may be deprecated. 81 * 82 * @param <R> the return type of this visitor's methods. Use {@link 83 * Void} for visitors that do not need to return results. 84 * @param <P> the type of the additional parameter to this visitor's 85 * methods. Use {@code Void} for visitors that do not need an 86 * additional parameter. 87 * 88 * @author Joseph D. Darcy 89 * @author Scott Seligman 90 * @author Peter von der Ahé 91 * 92 * @see ElementScanner7 93 * @see ElementScanner8 94 * @since 1.6 95 */ 96 @SupportedSourceVersion(RELEASE_6) 97 public class ElementScanner6<R, P> extends AbstractElementVisitor6<R, P> { 98 /** 99 * The specified default value. 100 */ 101 protected final R DEFAULT_VALUE; 102 103 /** 104 * Constructor for concrete subclasses; uses {@code null} for the 105 * default value. 106 */ 107 protected ElementScanner6(){ 108 DEFAULT_VALUE = null; 109 } 110 111 /** 112 * Constructor for concrete subclasses; uses the argument for the 113 * default value. 114 */ 115 protected ElementScanner6(R defaultValue){ 116 DEFAULT_VALUE = defaultValue; 117 } 118 119 /** 120 * Iterates over the given elements and calls {@link 121 * #scan(Element, Object) scan(Element, P)} on each one. Returns 122 * the result of the last call to {@code scan} or {@code 123 * DEFAULT_VALUE} for an empty iterable. 124 * 125 * @param iterable the elements to scan 126 * @param p additional parameter 127 * @return the scan of the last element or {@code DEFAULT_VALUE} if no elements 128 */ 129 public final R scan(Iterable<? extends Element> iterable, P p) { 130 R result = DEFAULT_VALUE; 131 for(Element e : iterable) 132 result = scan(e, p); 133 return result; 134 } 135 136 /** 137 * Processes an element by calling {@code e.accept(this, p)}; 138 * this method may be overridden by subclasses. 139 * @return the result of visiting {@code e}. 140 */ 141 public R scan(Element e, P p) { 142 return e.accept(this, p); 143 } 144 145 /** 146 * Convenience method equivalent to {@code v.scan(e, null)}. 147 * @return the result of scanning {@code e}. 148 */ 149 public final R scan(Element e) { 150 return scan(e, null); 151 } 152 153 /** 154 * {@inheritDoc} This implementation scans the enclosed elements. 155 * 156 * @param e {@inheritDoc} 157 * @param p {@inheritDoc} 158 * @return the result of scanning 159 */ 160 public R visitPackage(PackageElement e, P p) { 161 return scan(e.getEnclosedElements(), p); 162 } 163 164 /** 165 * {@inheritDoc} This implementation scans the enclosed elements. 166 * 167 * @param e {@inheritDoc} 168 * @param p {@inheritDoc} 169 * @return the result of scanning 170 */ 171 public R visitType(TypeElement e, P p) { 172 return scan(e.getEnclosedElements(), p); 173 } 174 175 /** 176 * {@inheritDoc} 177 * 178 * This implementation scans the enclosed elements, unless the 179 * element is a {@code RESOURCE_VARIABLE} in which case {@code 180 * visitUnknown} is called. 181 * 182 * @param e {@inheritDoc} 183 * @param p {@inheritDoc} 184 * @return the result of scanning 185 */ 186 public R visitVariable(VariableElement e, P p) { 187 if (e.getKind() != ElementKind.RESOURCE_VARIABLE) 188 return scan(e.getEnclosedElements(), p); 189 else 190 return visitUnknown(e, p); 191 } 192 193 /** 194 * {@inheritDoc} This implementation scans the parameters. 195 * 196 * @param e {@inheritDoc} 197 * @param p {@inheritDoc} 198 * @return the result of scanning 199 */ 200 public R visitExecutable(ExecutableElement e, P p) { 201 return scan(e.getParameters(), p); 202 } 203 204 /** 205 * {@inheritDoc} This implementation scans the enclosed elements. 206 * 207 * @param e {@inheritDoc} 208 * @param p {@inheritDoc} 209 * @return the result of scanning 210 */ 211 public R visitTypeParameter(TypeParameterElement e, P p) { 212 return scan(e.getEnclosedElements(), p); 213 } 214 }