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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *     http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.configuration2.tree;
18  
19  /**
20   * <p>
21   * Definition of a <em>Visitor</em> interface for a configuration node structure.
22   * </p>
23   * <p>
24   * This is a typical application of the GoF <em>Visitor</em> pattern. An object implementing this interface can be used
25   * to traverse a hierarchical structure of nodes in various ways. The type of the nodes in the structure is generic; a
26   * corresponding {@link NodeHandler} implementation must be available for navigating through the structure.
27   * </p>
28   * <p>
29   * Note that the exact way the methods of a {@code ConfigurationNodeVisitor} are invoked is dependent on a specific
30   * traversal process.
31   * </p>
32   *
33   * @since 1.3
34   * @param <T> the type of the nodes processed by this visitor
35   */
36  public interface ConfigurationNodeVisitor<T> {
37      /**
38       * Returns a flag whether the current visit process should be aborted. This method allows a visitor implementation to
39       * state that it does not need any further data. It may be used e.g. by visitors that search for a certain node in the
40       * hierarchy. After that node was found, there is no need to process the remaining nodes, too. This method is called
41       * after each visited node. A result of <strong>true</strong> indicates that the current iteration is to be aborted.
42       *
43       * @return a flag if the visit process should be stopped
44       */
45      boolean terminate();
46  
47      /**
48       * Visits the specified node after after its children - if existing - have been processed.
49       *
50       * @param node the node to be visited
51       * @param handler the {@code NodeHandler}
52       */
53      void visitAfterChildren(T node, NodeHandler<T> handler);
54  
55      /**
56       * Visits the specified node before the children of this node - if existing - are processed.
57       *
58       * @param node the node to be visited
59       * @param handler the {@code NodeHandler}
60       */
61      void visitBeforeChildren(T node, NodeHandler<T> handler);
62  }