001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.hbase;
020
021import java.io.IOException;
022
023import org.apache.yetus.audience.InterfaceAudience;
024
025/**
026 * An interface for iterating through a sequence of cells. Similar to Java's Iterator, but without
027 * the hasNext() or remove() methods. The hasNext() method is problematic because it may require
028 * actually loading the next object, which in turn requires storing the previous object somewhere.
029 *
030 * <p>The core data block decoder should be as fast as possible, so we push the complexity and
031 * performance expense of concurrently tracking multiple cells to layers above the CellScanner.
032 * <p>
033 * The {@link #current()} method will return a reference to a Cell implementation. This reference
034 * may or may not point to a reusable cell implementation, so users of the CellScanner should not,
035 * for example, accumulate a List of Cells. All of the references may point to the same object,
036 * which would be the latest state of the underlying Cell. In short, the Cell is mutable.
037 * </p>
038 * Typical usage:
039 *
040 * <pre>
041 * while (scanner.advance()) {
042 *   Cell cell = scanner.current();
043 *   // do something
044 * }
045 * </pre>
046 * <p>Often used reading {@link org.apache.hadoop.hbase.Cell}s written by
047 * {@link org.apache.hadoop.hbase.io.CellOutputStream}.
048 */
049@InterfaceAudience.Public
050public interface CellScanner {
051  /**
052   * @return the current Cell which may be mutable
053   */
054  Cell current();
055
056  /**
057   * Advance the scanner 1 cell.
058   * @return true if the next cell is found and {@link #current()} will return a valid Cell
059   * @throws IOException
060   */
061  boolean advance() throws IOException;
062}