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.hbase.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 }