001    /*
002     *  Licensed to the Apache Software Foundation (ASF) under one
003     *  or more contributor license agreements.  See the NOTICE file
004     *  distributed with this work for additional information
005     *  regarding copyright ownership.  The ASF licenses this file
006     *  to you under the Apache License, Version 2.0 (the
007     *  "License"); you may not use this file except in compliance
008     *  with the License.  You may obtain a copy of the License at
009     *  
010     *    http://www.apache.org/licenses/LICENSE-2.0
011     *  
012     *  Unless required by applicable law or agreed to in writing,
013     *  software distributed under the License is distributed on an
014     *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015     *  KIND, either express or implied.  See the License for the
016     *  specific language governing permissions and limitations
017     *  under the License. 
018     *  
019     */
020    package org.apache.directory.shared.ldap.filter;
021    
022    
023    import java.util.List;
024    
025    
026    /**
027     * Filter expression tree node visitor interface. Note that this is a variation
028     * of the extrinsic visitor variation. It has the following advantages over the
029     * standard visitor pattern:
030     * <ul>
031     * <li>Visitor takes responsibility that a visitor can visit a node</li>
032     * <li>Each visitor knows which types of concrete classes it can visit</li>
033     * <li>New visitors can be created without changing the node class</li>
034     * <li>New node classes can be added without having to change old visitors</li>
035     * <li>Visitation order can be controled in every respect:</li>
036     * <ul>
037     * <li>Visitation rejection with canVisit() and/or getOrder()</li>
038     * <li>Recursive visitation ordering with isPrefix()</li>
039     * <li>Child visitation ordering with getOrder()</li>
040     * </ul>
041     * </ul>
042     * 
043     * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
044     * @version $Revision: 664290 $
045     */
046    public interface FilterVisitor
047    {
048        /**
049         * Visits a filter expression AST using a specific visitation order.
050         * 
051         * @param node the node to visit
052         * @return node the resulting modified node
053         */
054        Object visit( ExprNode node );
055    
056    
057        /**
058         * Checks to see if a node can be visited.
059         * 
060         * @param node the node to be visited
061         * @return whether or node the node should be visited
062         */
063        boolean canVisit( ExprNode node );
064    
065    
066        /**
067         * Determines whether the visitation order is prefix or postfix.
068         * 
069         * @return true if the visitation is in prefix order, false otherwise.
070         */
071        boolean isPrefix();
072    
073    
074        /**
075         * Get the array of children to visit sequentially to determine the order of
076         * child visitations. Some children may not be returned at all if canVisit()
077         * returns false on them.
078         * 
079         * @param node the parent branch node
080         * @param children the child node array
081         * @return the new reordered array of children
082         */
083        List<ExprNode> getOrder( BranchNode node, List<ExprNode> children );
084    }