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
022 * structure.
023 * </p>
024 * <p>
025 * This is a typical application of the GoF <em>Visitor</em> pattern. An object
026 * implementing this interface can be used to traverse a hierarchical structure
027 * of nodes in various ways. The type of the nodes in the structure is generic;
028 * a corresponding {@link NodeHandler} implementation must be available for
029 * navigating through the structure.
030 * </p>
031 * <p>
032 * Note that the exact way the methods of a {@code ConfigurationNodeVisitor} are
033 * invoked is dependent on a specific traversal process.
034 * </p>
035 *
036 * @since 1.3
037 * @param <T> the type of the nodes processed by this visitor
038 */
039public interface ConfigurationNodeVisitor<T>
040{
041    /**
042     * Visits the specified node before the children of this node - if existing
043     * - are processed.
044     *
045     * @param node the node to be visited
046     * @param handler the {@code NodeHandler}
047     */
048    void visitBeforeChildren(T node, NodeHandler<T> handler);
049
050    /**
051     * Visits the specified node after after its children - if existing - have
052     * been processed.
053     *
054     * @param node the node to be visited
055     * @param handler the {@code NodeHandler}
056     */
057    void visitAfterChildren(T node, NodeHandler<T> handler);
058
059    /**
060     * Returns a flag whether the current visit process should be aborted. This
061     * method allows a visitor implementation to state that it does not need any
062     * further data. It may be used e.g. by visitors that search for a certain
063     * node in the hierarchy. After that node was found, there is no need to
064     * process the remaining nodes, too. This method is called after each
065     * visited node. A result of <strong>true</strong> indicates that the
066     * current iteration is to be aborted.
067     *
068     * @return a flag if the visit process should be stopped
069     */
070    boolean terminate();
071}