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; 20 21 import org.apache.hadoop.classification.InterfaceAudience; 22 import org.apache.hadoop.classification.InterfaceStability; 23 import org.apache.hadoop.hbase.Cell; 24 25 /** 26 * An interface for iterating through a sequence of cells. Similar to Java's Iterator, but without 27 * the hasNext() or remove() methods. The hasNext() method is problematic because it may require 28 * actually loading the next object, which in turn requires storing the previous object somewhere. 29 * 30 * <p>The core data block decoder should be as fast as possible, so we push the complexity and 31 * performance expense of concurrently tracking multiple cells to layers above the CellScanner. 32 * <p> 33 * The {@link #current()} method will return a reference to a Cell implementation. This reference 34 * may or may not point to a reusable cell implementation, so users of the CellScanner should not, 35 * for example, accumulate a List of Cells. All of the references may point to the same object, 36 * which would be the latest state of the underlying Cell. In short, the Cell is mutable. 37 * <p/> 38 * Typical usage: 39 * 40 * <pre> 41 * while (scanner.next()) { 42 * Cell cell = scanner.get(); 43 * // do something 44 * } 45 * </pre> 46 * <p>Often used reading {@link org.apache.hadoop.hbase.Cell}s written by 47 * {@link org.apache.hadoop.hbase.io.CellOutputStream}. 48 */ 49 @InterfaceAudience.Private 50 @InterfaceStability.Unstable 51 public interface CellScanner { 52 /** 53 * @return the current Cell which may be mutable 54 */ 55 Cell current(); 56 57 /** 58 * Advance the scanner 1 cell. 59 * @return true if the next cell is found and {@link #current()} will return a valid Cell 60 */ 61 boolean advance(); 62 }