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1   /*
2    *  Licensed to the Apache Software Foundation (ASF) under one
3    *  or more contributor license agreements.  See the NOTICE file
4    *  distributed with this work for additional information
5    *  regarding copyright ownership.  The ASF licenses this file
6    *  to you under the Apache License, Version 2.0 (the
7    *  "License"); you may not use this file except in compliance
8    *  with the License.  You may obtain a copy of the License at
9    *
10   *    http://www.apache.org/licenses/LICENSE-2.0
11   *
12   *  Unless required by applicable law or agreed to in writing,
13   *  software distributed under the License is distributed on an
14   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15   *  KIND, either express or implied.  See the License for the
16   *  specific language governing permissions and limitations
17   *  under the License.
18   *
19   */
20  package org.apache.directory.mavibot.btree.managed;
21  
22  
23  import java.io.IOException;
24  
25  import org.apache.directory.mavibot.btree.exception.EndOfFileExceededException;
26  
27  
28  /**
29   * A Value holder. As we may not store all the values in memory (except for an in-memory
30   * BTree), we will use a SoftReference to keep a reference to a Value, and if it's null,
31   * then we will load the Value from the underlying physical support, using the offset. 
32   * 
33   * @param <E> The type for the stored element (either a V or a Page<K, V>)
34   * @param <K> The type of the BTree key
35   * @param <V> The type of the BTree value
36   *
37   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
38   */
39  public interface ElementHolder<E, K, V>
40  {
41      /**
42       * Get back the element
43       * 
44       * @param btree The Btree storing the element
45       * 
46       * @return The stored element
47       */
48      E getValue( BTree<K, V> btree ) throws EndOfFileExceededException, IOException;
49  }