1 /*

     2  * Copyright 2005-2006 Sun Microsystems, Inc.  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.  Sun designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

    22  * CA 95054 USA or visit www.sun.com if you need additional information or

    23  * have any 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 }