1 /*
   2  * Copyright (c) 2006, 2016, 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 com.sun.source.util;
  27 
  28 import com.sun.source.tree.*;
  29 
  30 /**
  31  * A TreeVisitor that visits all the child tree nodes, and provides
  32  * support for maintaining a path for the parent nodes.
  33  * To visit nodes of a particular type, just override the
  34  * corresponding visitorXYZ method.
  35  * Inside your method, call super.visitXYZ to visit descendant
  36  * nodes.
  37  *
  38  * @apiNote
  39  * In order to initialize the "current path", the scan must be
  40  * started by calling one of the {@code scan} methods.
  41  *
  42  * @author Jonathan Gibbons
  43  * @since 1.6
  44  */
  45 public class TreePathScanner<R, P> extends TreeScanner<R, P> {
  46 
  47     /**
  48      * Scans a tree from a position identified by a TreePath.
  49      * @param path the path identifying the node to be scanned
  50      * @param p a parameter value passed to visit methods
  51      * @return the result value from the visit method
  52      */
  53     public R scan(TreePath path, P p) {
  54         this.path = path;
  55         try {
  56             return path.getLeaf().accept(this, p);
  57         } finally {
  58             this.path = null;
  59         }
  60     }
  61 
  62     /**
  63      * Scans a single node.
  64      * The current path is updated for the duration of the scan.
  65      *
  66      * @apiNote This method should normally only be called by the
  67      * scanner's {@code visit} methods, as part of an ongoing scan
  68      * initiated by {@link #scan(TreePath,Object) scan(TreePath, P)}.
  69      * The one exception is that it may also be called to initiate
  70      * a full scan of a {@link CompilationUnitTree}.
  71      *
  72      * @return the result value from the visit method
  73      */
  74     @Override
  75     public R scan(Tree tree, P p) {
  76         if (tree == null)
  77             return null;
  78 
  79         TreePath prev = path;
  80         path = new TreePath(path, tree);
  81         try {
  82             return tree.accept(this, p);
  83         } finally {
  84             path = prev;
  85         }
  86     }
  87 
  88     /**
  89      * Returns the current path for the node, as built up by the currently
  90      * active set of scan calls.
  91      * @return the current path
  92      */
  93     public TreePath getCurrentPath() {
  94         return path;
  95     }
  96 
  97     private TreePath path;
  98 }