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1   /**
2    * Copyright 2010 The Apache Software Foundation
3    *
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *     http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing, software
15   * distributed under the License is distributed on an "AS IS" BASIS,
16   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17   * See the License for the specific language governing permissions and
18   * limitations under the License.
19   */
20  package org.apache.hadoop.hbase.regionserver;
21  
22  import java.io.IOException;
23  
24  import org.apache.hadoop.hbase.KeyValue;
25  
26  /**
27   * Scanner that returns the next KeyValue.
28   */
29  public interface KeyValueScanner {
30    /**
31     * Look at the next KeyValue in this scanner, but do not iterate scanner.
32     * @return the next KeyValue
33     */
34    public KeyValue peek();
35  
36    /**
37     * Return the next KeyValue in this scanner, iterating the scanner
38     * @return the next KeyValue
39     */
40    public KeyValue next() throws IOException;
41  
42    /**
43     * Seek the scanner at or after the specified KeyValue.
44     * @param key seek value
45     * @return true if scanner has values left, false if end of scanner
46     */
47    public boolean seek(KeyValue key) throws IOException;
48  
49    /**
50     * Reseek the scanner at or after the specified KeyValue.
51     * This method is guaranteed to seek to or before the required key only if the
52     * key comes after the current position of the scanner. Should not be used
53     * to seek to a key which may come before the current position.
54     * @param key seek value (should be non-null)
55     * @return true if scanner has values left, false if end of scanner
56     */
57    public boolean reseek(KeyValue key) throws IOException;
58  
59    /**
60     * Get the sequence id associated with this KeyValueScanner. This is required
61     * for comparing multiple files to find out which one has the latest data.
62     * The default implementation for this would be to return 0. A file having
63     * lower sequence id will be considered to be the older one.
64     */
65    public long getSequenceID();
66  
67    /**
68     * Close the KeyValue scanner.
69     */
70    public void close();
71  }