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 package org.apache.hadoop.hbase.classification;
19
20 import java.lang.annotation.Documented;
21 import java.lang.annotation.Retention;
22 import java.lang.annotation.RetentionPolicy;
23
24 /**
25 * Annotation to inform users of a package, class or method's intended audience.
26 * Currently the audience can be {@link Public}, {@link LimitedPrivate} or
27 * {@link Private}. <br>
28 * All public classes must have InterfaceAudience annotation. <br>
29 * <ul>
30 * <li>Public classes that are not marked with this annotation must be
31 * considered by default as {@link Private}.</li>
32 *
33 * <li>External applications must only use classes that are marked
34 * {@link Public}. Avoid using non public classes as these classes
35 * could be removed or change in incompatible ways.</li>
36 *
37 * <li>Hadoop projects must only use classes that are marked
38 * {@link LimitedPrivate} or {@link Public}</li>
39 *
40 * <li> Methods may have a different annotation that it is more restrictive
41 * compared to the audience classification of the class. Example: A class
42 * might be {@link Public}, but a method may be {@link LimitedPrivate}
43 * </li></ul>
44 */
45 @InterfaceAudience.Public
46 @InterfaceStability.Evolving
47 public class InterfaceAudience {
48 /**
49 * Intended for use by any project or application.
50 */
51 @Documented
52 @Retention(RetentionPolicy.RUNTIME)
53 public @interface Public {};
54
55 /**
56 * Intended only for the project(s) specified in the annotation.
57 * For example, "Common", "HDFS", "MapReduce", "ZooKeeper", "HBase".
58 */
59 @Documented
60 @Retention(RetentionPolicy.RUNTIME)
61 public @interface LimitedPrivate {
62 String[] value();
63 };
64
65 /**
66 * Intended for use only within Hadoop itself.
67 */
68 @Documented
69 @Retention(RetentionPolicy.RUNTIME)
70 public @interface Private {};
71
72 private InterfaceAudience() {} // Audience can't exist on its own
73 }