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 * 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

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

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 * 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

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package com.sun.source.util;

import com.sun.source.tree.*;

import com.sun.source.tree.CaseTree.CaseKind;

/**

 * 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 identifier nodes in a tree:

 * <pre>

 *   class CountIdentifiers extends TreeScanner<Integer,Void> {

 *      {@literal @}Override

 *      public Integer visitIdentifier(IdentifierTree node, Void p) {

 *          return 1;

 *      }

 *      {@literal @}Override

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

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

 *      }

 *   }

 * </pre>

 *

 * @param <R> the return type of this visitor's methods.  Use {@link

 *            Void} for visitors that do not need to return results.

 * @param <P> the type of the additional parameter to this visitor's

 *            methods.  Use {@code Void} for visitors that do not need an

 *            additional parameter.

 *

 * @author Peter von der Ahé

 * @author Jonathan Gibbons

 * @since 1.6

 */

public class TreeScanner<R,P> implements TreeVisitor<R,P> {

    /**

     * Scans a single node.

     * @param tree 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(Tree tree, P p) {

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

    }

    private R scanAndReduce(Tree 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 Tree> nodes, P p) {

        R r = null;

        if (nodes != null) {

            boolean first = true;

            for (Tree node : nodes) {

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

                first = false;

            }

        }

        return r;

    }

    private R scanAndReduce(Iterable<? extends Tree> 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 scans the children in left to right order.

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitCompilationUnit(CompilationUnitTree node, P p) {

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

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

        r = scanAndReduce(node.getTypeDecls(), 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 visitPackage(PackageTree node, P p) {

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

        r = scanAndReduce(node.getPackageName(), 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 visitImport(ImportTree node, P p) {

        return scan(node.getQualifiedIdentifier(), 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 visitClass(ClassTree node, P p) {

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

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

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

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

        r = scanAndReduce(node.getMembers(), 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 visitMethod(MethodTree node, P p) {

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

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

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

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

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

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

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

        r = scanAndReduce(node.getDefaultValue(), 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 visitVariable(VariableTree node, P p) {

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

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

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

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

        return r;

    }

    /**

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

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitEmptyStatement(EmptyStatementTree 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 visitBlock(BlockTree node, P p) {

        return scan(node.getStatements(), 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 visitDoWhileLoop(DoWhileLoopTree node, P p) {

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

        r = scanAndReduce(node.getCondition(), 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 visitWhileLoop(WhileLoopTree node, P p) {

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

        r = scanAndReduce(node.getStatement(), 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 visitForLoop(ForLoopTree node, P p) {

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

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

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

        r = scanAndReduce(node.getStatement(), 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 visitEnhancedForLoop(EnhancedForLoopTree node, P p) {

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

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

        r = scanAndReduce(node.getStatement(), 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 visitLabeledStatement(LabeledStatementTree node, P p) {

        return scan(node.getStatement(), 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 visitSwitch(SwitchTree node, P p) {

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

        r = scanAndReduce(node.getCases(), 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

     *

     * @deprecated

     * This method is modeling switch expressions,

     * which are part of a preview feature and may be removed

     * if the preview feature is removed.

     */

    @Override

    @Deprecated(forRemoval=true, since="12")

    @SuppressWarnings("removal")

    public R visitSwitchExpression(SwitchExpressionTree node, P p) {

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

        r = scanAndReduce(node.getCases(), 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

    @SuppressWarnings("removal")

    public R visitCase(CaseTree node, P p) {

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

        if (node.getCaseKind() == CaseKind.RULE)

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

        else

            r = scanAndReduce(node.getStatements(), 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 visitSynchronized(SynchronizedTree node, P p) {

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

        r = scanAndReduce(node.getBlock(), 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 visitTry(TryTree node, P p) {

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

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

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

        r = scanAndReduce(node.getFinallyBlock(), 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 visitCatch(CatchTree node, P p) {

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

        r = scanAndReduce(node.getBlock(), 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 visitConditionalExpression(ConditionalExpressionTree node, P p) {

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

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

        r = scanAndReduce(node.getFalseExpression(), 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 visitIf(IfTree node, P p) {

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

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

        r = scanAndReduce(node.getElseStatement(), 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 visitExpressionStatement(ExpressionStatementTree node, P p) {

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

    }

    /**

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

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitBreak(BreakTree node, P p) {

    }

    /**

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

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */

    @Override

    public R visitContinue(ContinueTree 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.getExpression(), p);

    }

    /**

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

     *

     * @param node  {@inheritDoc}

     * @param p  {@inheritDoc}

     * @return the result of scanning

     */