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.hbase.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 }