1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 *
19 */
20 package org.apache.directory.api.ldap.model.filter;
21
22
23 import java.util.List;
24
25
26 /**
27 * Filter expression tree node visitor interface. Note that this is a variation
28 * of the extrinsic visitor variation. It has the following advantages over the
29 * standard visitor pattern:
30 * <ul>
31 * <li>Visitor takes responsibility that a visitor can visit a node</li>
32 * <li>Each visitor knows which types of concrete classes it can visit</li>
33 * <li>New visitors can be created without changing the node class</li>
34 * <li>New node classes can be added without having to change old visitors</li>
35 * <li>Visitation order can be controled in every respect:</li>
36 * <ul>
37 * <li>Visitation rejection with canVisit() and/or getOrder()</li>
38 * <li>Recursive visitation ordering with isPrefix()</li>
39 * <li>Child visitation ordering with getOrder()</li>
40 * </ul>
41 * </ul>
42 *
43 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
44 */
45 public interface FilterVisitor
46 {
47 /**
48 * Visits a filter expression AST using a specific visitation order.
49 *
50 * @param node the node to visit
51 * @return node the resulting modified node
52 */
53 Object visit( ExprNode node );
54
55
56 /**
57 * Checks to see if a node can be visited.
58 *
59 * @param node the node to be visited
60 * @return whether or node the node should be visited
61 */
62 boolean canVisit( ExprNode node );
63
64
65 /**
66 * Determines whether the visitation order is prefix or postfix.
67 *
68 * @return true if the visitation is in prefix order, false otherwise.
69 */
70 boolean isPrefix();
71
72
73 /**
74 * Get the array of children to visit sequentially to determine the order of
75 * child visitations. Some children may not be returned at all if canVisit()
76 * returns false on them.
77 *
78 * @param node the parent branch node
79 * @param children the child node array
80 * @return the new reordered array of children
81 */
82 List<ExprNode> getOrder( BranchNode node, List<ExprNode> children );
83 }