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     */
017    package org.apache.commons.configuration.tree;
018    
019    /**
020     * <p>
021     * Definition of a <em>Visitor</em> interface for a configuration node
022     * structure.
023     * </p>
024     * <p>
025     * The <code>ConfigurationNode</code> interface defines a <code>visit()</code>,
026     * which simplifies traversal of a complex node hierarchy. A configuration node
027     * implementation must provide a way of visiting all nodes in the current
028     * hierarchy. This is a typical application of the GoF <em>Visitor</em>
029     * pattern.
030     * </p>
031     *
032     * @since 1.3
033     * @see ConfigurationNode
034     * @author Oliver Heger
035     */
036    public interface ConfigurationNodeVisitor
037    {
038        /**
039         * Visits the specified node. This method is called before eventually
040         * existing children of this node are processed.
041         *
042         * @param node the node to be visited
043         */
044        void visitBeforeChildren(ConfigurationNode node);
045    
046        /**
047         * Visits the specified node. This method is called after eventually
048         * existing children of this node have been processed.
049         *
050         * @param node the node to be visited
051         */
052        void visitAfterChildren(ConfigurationNode node);
053    
054        /**
055         * Returns a flag whether the actual visit process should be aborted. This
056         * method allows a visitor implementation to state that it does not need any
057         * further data. It may be used e.g. by visitors that search for a certain
058         * node in the hierarchy. After that node was found, there is no need to
059         * process the remaining nodes, too.
060         *
061         * @return a flag if the visit process should be stopped
062         */
063        boolean terminate();
064    }