View Javadoc

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.io.util;
20  
21  import org.apache.hadoop.classification.InterfaceAudience;
22  
23  /**
24   * Dictionary interface
25   *
26   * Dictionary indexes should be either bytes or shorts, only positive. (The
27   * first bit is reserved for detecting whether something is compressed or not).
28   */
29  @InterfaceAudience.Private
30  public interface Dictionary {
31    byte NOT_IN_DICTIONARY = -1;
32  
33    void init(int initialSize);
34    /**
35     * Gets an entry from the dictionary.
36     * 
37     * @param idx index of the entry
38     * @return the entry, or null if non existent
39     */
40    byte[] getEntry(short idx);
41  
42    /**
43     * Finds the index of an entry.
44     * If no entry found, we add it.
45     * 
46     * @param data the byte array that we're looking up
47     * @param offset Offset into <code>data</code> to add to Dictionary.
48     * @param length Length beyond <code>offset</code> that comprises entry; must be > 0.
49     * @return the index of the entry, or {@link #NOT_IN_DICTIONARY} if not found
50     */
51    short findEntry(byte[] data, int offset, int length);
52  
53    /**
54     * Adds an entry to the dictionary.
55     * Be careful using this method.  It will add an entry to the
56     * dictionary even if it already has an entry for the same data.
57     * Call {{@link #findEntry(byte[], int, int)}} to add without duplicating
58     * dictionary entries.
59     * 
60     * @param data the entry to add
61     * @param offset Offset into <code>data</code> to add to Dictionary.
62     * @param length Length beyond <code>offset</code> that comprises entry; must be > 0.
63     * @return the index of the entry
64     */
65  
66    short addEntry(byte[] data, int offset, int length);
67  
68    /**
69     * Flushes the dictionary, empties all values.
70     */
71    void clear();
72  }