TreePathScanner.java revision 3687:8e011f635081 
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
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24 */
25
26package com.sun.source.util;
27
28import 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 */
45public 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}
99