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.hbase.codec.prefixtree.scanner;
20
21 import org.apache.hadoop.classification.InterfaceAudience;
22
23 /**
24 * An extension of CellScanner indicating the scanner supports iterating backwards through cells.
25 * <p>
26 * Note: This was not added to suggest that HBase should support client facing reverse Scanners, but
27 * because some {@link CellSearcher} implementations, namely PrefixTree, need a method of backing up
28 * if the positionAt(..) method goes past the requested cell.
29 */
30 @InterfaceAudience.Private
31 public interface ReversibleCellScanner extends CellScanner {
32
33 /**
34 * Try to position the scanner one Cell before the current position.
35 * @return true if the operation was successful, meaning getCurrentCell() will return a valid
36 * Cell.<br/>
37 * false if there were no previous cells, meaning getCurrentCell() will return null.
38 * Scanner position will be {@link org.apache.hbase.cell.CellScannerPosition#BEFORE_FIRST}
39 */
40 boolean previous();
41
42 /**
43 * Try to position the scanner in the row before the current row.
44 * @param endOfRow true for the last cell in the previous row; false for the first cell
45 * @return true if the operation was successful, meaning getCurrentCell() will return a valid
46 * Cell.<br/>
47 * false if there were no previous cells, meaning getCurrentCell() will return null.
48 * Scanner position will be {@link org.apache.hbase.cell.CellScannerPosition#BEFORE_FIRST}
49 */
50 boolean previousRow(boolean endOfRow);
51
52 }