1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.configuration2.tree;
18
19 import java.util.List;
20
21 /**
22 * <p>
23 * An extension of the {@link NodeHandler} interface which allows access to so-called <em>references</em> stored for a
24 * node.
25 * </p>
26 * <p>
27 * Some specialized configuration implementations needs to store additional data for the nodes representing
28 * configuration properties. This interface provides methods for querying this data. For instance, it is possible to
29 * query a reference object stored for a specific node.
30 * </p>
31 * <p>
32 * {@link InMemoryNodeModel} supports references. It can be queried for a {@code ReferenceNodeHandler} which can then be
33 * used for dealing with references.
34 * </p>
35 *
36 * @since 2.0
37 */
38 public interface ReferenceNodeHandler extends NodeHandler<ImmutableNode> {
39 /**
40 * Gets the reference object associated with the specified node. If no reference data is associated with this node,
41 * result is <b>null</b>.
42 *
43 * @param node the node in question
44 * @return the reference object for this node or <b>null</b>
45 */
46 Object getReference(ImmutableNode node);
47
48 /**
49 * Returns a list with the reference objects for nodes which have been removed. Whenever a node associated with a
50 * reference object is removed from the nodes structure managed by the owning model, the reference object is recorded.
51 * This is necessary for instance to free some resources. With this method all recorded reference objects can be
52 * queried. They are typically returned in the order in which they have been removed.
53 *
54 * @return a list with reference objects for nodes removed from the model
55 */
56 List<Object> removedReferences();
57 }