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&trade; 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 Ah&eacute;
  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 }