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 * Copyright (c) 2011, 2017, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

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

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package com.sun.source.util;

import com.sun.source.doctree.*;

/**

 * A TreeVisitor that visits all the child tree nodes.

 * To visit nodes of a particular type, just override the

 * corresponding visitXYZ method.

 * Inside your method, call super.visitXYZ to visit descendant

 * nodes.

 *

 * <p>The default implementation of the visitXYZ methods will determine

 * a result as follows:

 * <ul>

 * <li>If the node being visited has no children, the result will be {@code null}.

 * <li>If the node being visited has one child, the result will be the

 * result of calling {@code scan} on that child. The child may be a simple node

 * or itself a list of nodes.

 * <li> If the node being visited has more than one child, the result will

 * be determined by calling {@code scan} each child in turn, and then combining the

 * result of each scan after the first with the cumulative result

 * so far, as determined by the {@link #reduce} method. Each child may be either

 * a simple node of a list of nodes. The default behavior of the {@code reduce}

 * method is such that the result of the visitXYZ method will be the result of

 * the last child scanned.

 * </ul>

 *

 * <p>Here is an example to count the number of erroneous nodes in a tree:

 * <pre>

 *   class CountErrors extends DocTreeScanner<Integer,Void> {

 *      {@literal @}Override

 *      public Integer visitErroneous(ErroneousTree node, Void p) {

 *          return 1;

 *      }

 *      {@literal @}Override

 *      public Integer reduce(Integer r1, Integer r2) {

 *          return (r1 == null ? 0 : r1) + (r2 == null ? 0 : r2);

 *      }

 *   }

 * </pre>

 *

 * @since 1.8

 */

public class DocTreeScanner<R,P> implements DocTreeVisitor<R,P> {

    /**

     * Scans a single node.

     * @param node the node to be scanned

     * @param p a parameter value passed to the visit method

     * @return the result value from the visit method

     */

    public R scan(DocTree node, P p) {

        return (node == null) ? null : node.accept(this, p);

    }

    private R scanAndReduce(DocTree node, P p, R r) {

        return reduce(scan(node, p), r);

    }

    /**

     * Scans a sequence of nodes.

     * @param nodes the nodes to be scanned

     * @param p a parameter value to be passed to the visit method for each node

     * @return the combined return value from the visit methods.

     *      The values are combined using the {@link #reduce reduce} method.

     */

    public R scan(Iterable<? extends DocTree> nodes, P p) {

        R r = null;

        if (nodes != null) {

            boolean first = true;

            for (DocTree node : nodes) {

                r = (first ? scan(node, p) : scanAndReduce(node, p, r));

                first = false;

            }

        }

        return r;

    }

    private R scanAndReduce(Iterable<? extends DocTree> nodes, P p, R r) {

        return reduce(scan(nodes, p), r);

    }

    /**

     * Reduces two results into a combined result.

     * The default implementation is to return the first parameter.

     * The general contract of the method is that it may take any action whatsoever.

     * @param r1 the first of the values to be combined

     * @param r2 the second of the values to be combined

     * @return the result of combining the two parameters

     */

    public R reduce(R r1, R r2) {

        return r1;

    }

/* ***************************************************************************

 * Visitor methods

 ****************************************************************************/

    /**

     * {@inheritDoc} This implementation returns {@code null}.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitAttribute(AttributeTree node, P p) {

        return null;

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitAuthor(AuthorTree node, P p) {

        return scan(node.getName(), p);

    }

    /**

     * {@inheritDoc} This implementation returns {@code null}.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitComment(CommentTree node, P p) {

        return null;

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitDeprecated(DeprecatedTree node, P p) {

        return scan(node.getBody(), p);

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitDocComment(DocCommentTree node, P p) {

        R r = scan(node.getFirstSentence(), p);

        r = scanAndReduce(node.getBody(), p, r);

        r = scanAndReduce(node.getBlockTags(), p, r);

        return r;

    }

    /**

     * {@inheritDoc} This implementation returns {@code null}.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitDocRoot(DocRootTree node, P p) {

        return null;

    }

    /**

     * {@inheritDoc} This implementation returns {@code null}.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitDocType(DocTypeTree node, P p) {

        return null;

    }

    /**

     * {@inheritDoc} This implementation returns {@code null}.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitEndElement(EndElementTree node, P p) {

        return null;

    }

    /**

     * {@inheritDoc} This implementation returns {@code null}.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitEntity(EntityTree node, P p) {

        return null;

    }

    /**

     * {@inheritDoc} This implementation returns {@code null}.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitErroneous(ErroneousTree node, P p) {

        return null;

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitHidden(HiddenTree node, P p) {

        return scan(node.getBody(), p);

    }

    /**

     * {@inheritDoc} This implementation returns {@code null}.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitIdentifier(IdentifierTree node, P p) {

        return null;

    }

    /**

     * {@inheritDoc} This implementation returns {@code null}.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitIndex(IndexTree node, P p) {

        R r = scan(node.getSearchTerm(), p);

        r = scanAndReduce(node.getDescription(), p, r);

        return r;

    }

    /**

     * {@inheritDoc} This implementation returns {@code null}.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitInheritDoc(InheritDocTree node, P p) {

        return null;

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitLink(LinkTree node, P p) {

        R r = scan(node.getReference(), p);

        r = scanAndReduce(node.getLabel(), p, r);

        return r;

    }

    /**

     * {@inheritDoc} This implementation returns {@code null}.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitLiteral(LiteralTree node, P p) {

        return null;

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitParam(ParamTree node, P p) {

        R r = scan(node.getName(), p);

        r = scanAndReduce(node.getDescription(), p, r);

        return r;

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitProvides(ProvidesTree node, P p) {

        R r = scan(node.getServiceType(), p);

        r = scanAndReduce(node.getDescription(), p, r);

        return r;

    }

    /**

     * {@inheritDoc} This implementation returns {@code null}.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitReference(ReferenceTree node, P p) {

        return null;

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitReturn(ReturnTree node, P p) {

        return scan(node.getDescription(), p);

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitSee(SeeTree node, P p) {

        return scan(node.getReference(), p);

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitSerial(SerialTree node, P p) {

        return scan(node.getDescription(), p);

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitSerialData(SerialDataTree node, P p) {

        return scan(node.getDescription(), p);

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitSerialField(SerialFieldTree node, P p) {

        R r = scan(node.getName(), p);

        r = scanAndReduce(node.getType(), p, r);

        r = scanAndReduce(node.getDescription(), p, r);

        return r;

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitSince(SinceTree node, P p) {

        return scan(node.getBody(), p);

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitStartElement(StartElementTree node, P p) {

        return scan(node.getAttributes(), p);

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     * @since 10

     */

    @Override

    public R visitSummary(SummaryTree node, P p) {

        R r = scan(node.getSummary(), p);

        return r;

    }

    /**

     * {@inheritDoc} This implementation returns {@code null}.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitText(TextTree node, P p) {

        return null;

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitThrows(ThrowsTree node, P p) {

        R r = scan(node.getExceptionName(), p);

        r = scanAndReduce(node.getDescription(), p, r);

        return r;

    }

    /**

     * {@inheritDoc} This implementation scans the children in left to right order.