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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, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  package org.apache.hadoop.hbase.codec.prefixtree.scanner;
20  
21  import org.apache.hadoop.classification.InterfaceAudience;
22  import org.apache.hadoop.hbase.CellScanner;
23  
24  /**
25   * An extension of CellScanner indicating the scanner supports iterating backwards through cells.
26   * <p>
27   * Note: This was not added to suggest that HBase should support client facing reverse Scanners,
28   * but
29   * because some {@link CellSearcher} implementations, namely PrefixTree, need a method of backing
30   * up if the positionAt(..) method goes past the requested cell.
31   */
32  @InterfaceAudience.Private
33  public interface ReversibleCellScanner extends CellScanner {
34  
35    /**
36     * Try to position the scanner one Cell before the current position.
37     * @return true if the operation was successful, meaning getCurrentCell() will return a valid
38     *         Cell.<br/>
39     *         false if there were no previous cells, meaning getCurrentCell() will return null.
40     *         Scanner position will be
41     *         {@link org.apache.hadoop.hbase.codec.prefixtree.scanner.CellScannerPosition#BEFORE_FIRST}
42     */
43    boolean previous();
44  
45    /**
46     * Try to position the scanner in the row before the current row.
47     * @param endOfRow true for the last cell in the previous row; false for the first cell
48     * @return true if the operation was successful, meaning getCurrentCell() will return a valid
49     *         Cell.<br/>
50     *         false if there were no previous cells, meaning getCurrentCell() will return null.
51     *         Scanner position will be
52     *         {@link org.apache.hadoop.hbase.codec.prefixtree.scanner.CellScannerPosition#BEFORE_FIRST}
53     */
54    boolean previousRow(boolean endOfRow);
55  }