001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.configuration2.tree;
018
019/**
020 * <p>
021 * Definition of a <em>Visitor</em> interface for a configuration node structure.
022 * </p>
023 * <p>
024 * This is a typical application of the GoF <em>Visitor</em> pattern. An object implementing this interface can be used
025 * to traverse a hierarchical structure of nodes in various ways. The type of the nodes in the structure is generic; a
026 * corresponding {@link NodeHandler} implementation must be available for navigating through the structure.
027 * </p>
028 * <p>
029 * Note that the exact way the methods of a {@code ConfigurationNodeVisitor} are invoked is dependent on a specific
030 * traversal process.
031 * </p>
032 *
033 * @since 1.3
034 * @param <T> the type of the nodes processed by this visitor
035 */
036public interface ConfigurationNodeVisitor<T> {
037    /**
038     * Returns a flag whether the current visit process should be aborted. This method allows a visitor implementation to
039     * 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
040     * hierarchy. After that node was found, there is no need to process the remaining nodes, too. This method is called
041     * after each visited node. A result of <strong>true</strong> indicates that the current iteration is to be aborted.
042     *
043     * @return a flag if the visit process should be stopped
044     */
045    boolean terminate();
046
047    /**
048     * Visits the specified node after after its children - if existing - have been processed.
049     *
050     * @param node the node to be visited
051     * @param handler the {@code NodeHandler}
052     */
053    void visitAfterChildren(T node, NodeHandler<T> handler);
054
055    /**
056     * Visits the specified node before the children of this node - if existing - are processed.
057     *
058     * @param node the node to be visited
059     * @param handler the {@code NodeHandler}
060     */
061    void visitBeforeChildren(T node, NodeHandler<T> handler);
062}