1 /* 2 * Copyright (c) 2005, 2010, 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 * @since 1.6 94 */ 95 @SupportedSourceVersion(RELEASE_6) 96 public class ElementScanner6<R, P> extends AbstractElementVisitor6<R, P> { 97 /** 98 * The specified default value. 99 */ 100 protected final R DEFAULT_VALUE; 101 102 /** 103 * Constructor for concrete subclasses; uses {@code null} for the 104 * default value. 105 */ 106 protected ElementScanner6(){ 107 DEFAULT_VALUE = null; 108 } 109 110 /** 111 * Constructor for concrete subclasses; uses the argument for the 112 * default value. 113 */ 114 protected ElementScanner6(R defaultValue){ 115 DEFAULT_VALUE = defaultValue; 116 } 117 118 /** 119 * Iterates over the given elements and calls {@link 120 * #scan(Element, Object) scan(Element, P)} on each one. Returns 121 * the result of the last call to {@code scan} or {@code 122 * DEFAULT_VALUE} for an empty iterable. 123 * 124 * @param iterable the elements to scan 125 * @param p additional parameter 126 * @return the scan of the last element or {@code DEFAULT_VALUE} if no elements 127 */ 128 public final R scan(Iterable<? extends Element> iterable, P p) { 129 R result = DEFAULT_VALUE; 130 for(Element e : iterable) 131 result = scan(e, p); 132 return result; 133 } 134 135 /** 136 * Processes an element by calling {@code e.accept(this, p)}; 137 * this method may be overridden by subclasses. 138 * @return the result of visiting {@code e}. 139 */ 140 public R scan(Element e, P p) { 141 return e.accept(this, p); 142 } 143 144 /** 145 * Convenience method equivalent to {@code v.scan(e, null)}. 146 * @return the result of scanning {@code e}. 147 */ 148 public final R scan(Element e) { 149 return scan(e, null); 150 } 151 152 /** 153 * {@inheritDoc} This implementation scans the enclosed elements. 154 * 155 * @param e {@inheritDoc} 156 * @param p {@inheritDoc} 157 * @return the result of scanning 158 */ 159 public R visitPackage(PackageElement e, P p) { 160 return scan(e.getEnclosedElements(), p); 161 } 162 163 /** 164 * {@inheritDoc} This implementation scans the enclosed elements. 165 * 166 * @param e {@inheritDoc} 167 * @param p {@inheritDoc} 168 * @return the result of scanning 169 */ 170 public R visitType(TypeElement e, P p) { 171 return scan(e.getEnclosedElements(), p); 172 } 173 174 /** 175 * {@inheritDoc} 176 * 177 * This implementation scans the enclosed elements, unless the 178 * element is a {@code RESOURCE_VARIABLE} in which case {@code 179 * visitUnknown} is called. 180 * 181 * @param e {@inheritDoc} 182 * @param p {@inheritDoc} 183 * @return the result of scanning 184 */ 185 public R visitVariable(VariableElement e, P p) { 186 if (e.getKind() != ElementKind.RESOURCE_VARIABLE) 187 return scan(e.getEnclosedElements(), p); 188 else 189 return visitUnknown(e, p); 190 } 191 192 /** 193 * {@inheritDoc} This implementation scans the parameters. 194 * 195 * @param e {@inheritDoc} 196 * @param p {@inheritDoc} 197 * @return the result of scanning 198 */ 199 public R visitExecutable(ExecutableElement e, P p) { 200 return scan(e.getParameters(), p); 201 } 202 203 /** 204 * {@inheritDoc} This implementation scans the enclosed elements. 205 * 206 * @param e {@inheritDoc} 207 * @param p {@inheritDoc} 208 * @return the result of scanning 209 */ 210 public R visitTypeParameter(TypeParameterElement e, P p) { 211 return scan(e.getEnclosedElements(), p); 212 } 213 }