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 019import java.util.List; 020 021/** 022 * <p> 023 * An extension of the {@link NodeHandler} interface which allows access to 024 * so-called <em>references</em> stored for a node. 025 * </p> 026 * <p> 027 * Some specialized configuration implementations needs to store additional data 028 * for the nodes representing configuration properties. This interface provides 029 * methods for querying this data. For instance, it is possible to query a 030 * reference object stored for a specific node. 031 * </p> 032 * <p> 033 * {@link InMemoryNodeModel} supports references. It can be queried for a 034 * {@code ReferenceNodeHandler} which can then be used for dealing with 035 * references. 036 * </p> 037 * 038 * @since 2.0 039 */ 040public interface ReferenceNodeHandler extends NodeHandler<ImmutableNode> 041{ 042 /** 043 * Returns the reference object associated with the specified node. If no 044 * reference data is associated with this node, result is <b>null</b>. 045 * 046 * @param node the node in question 047 * @return the reference object for this node or <b>null</b> 048 */ 049 Object getReference(ImmutableNode node); 050 051 /** 052 * Returns a list with the reference objects for nodes which have been 053 * removed. Whenever a node associated with a reference object is removed 054 * from the nodes structure managed by the owning model, the reference 055 * object is recorded. This is necessary for instance to free some 056 * resources. With this method all recorded reference objects can be 057 * queried. They are typically returned in the order in which they have been 058 * removed. 059 * 060 * @return a list with reference objects for nodes removed from the model 061 */ 062 List<Object> removedReferences(); 063}