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 }