    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     * Visits the specified node before the children of this node - if existing - are processed.
    039     *
    040     * @param node the node to be visited
    041     * @param handler the {@code NodeHandler}
    042     */
    043    void visitBeforeChildren(T node, NodeHandler<T> handler);
    044
    045    /**
    046     * Visits the specified node after after its children - if existing - have been processed.
    047     *
    048     * @param node the node to be visited
    049     * @param handler the {@code NodeHandler}
    050     */
    051    void visitAfterChildren(T node, NodeHandler<T> handler);
    052
    053    /**
    054     * Returns a flag whether the current visit process should be aborted. This method allows a visitor implementation to
    055     * 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
    056     * hierarchy. After that node was found, there is no need to process the remaining nodes, too. This method is called
    057     * after each visited node. A result of <strong>true</strong> indicates that the current iteration is to be aborted.
    058     *
    059     * @return a flag if the visit process should be stopped
    060     */
    061    boolean terminate();
    062}