1 /* 2 * Copyright (c) 2005, 2006, 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 * @since 1.6 92 */ 93 @SupportedSourceVersion(RELEASE_6) 94 public class ElementScanner6<R, P> extends AbstractElementVisitor6<R, P> { 95 /** 96 * The specified default value. 97 */ 98 protected final R DEFAULT_VALUE; 99 100 /** 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 }