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 */ 018package org.apache.hadoop.classification; 019 020import java.lang.annotation.Documented; 021import java.lang.annotation.Retention; 022import java.lang.annotation.RetentionPolicy; 023 024/** 025 * Annotation to inform users of a package, class or method's intended audience. 026 * Currently the audience can be {@link Public}, {@link LimitedPrivate} or 027 * {@link Private}. <br> 028 * All public classes must have InterfaceAudience annotation. <br> 029 * <ul> 030 * <li>Public classes that are not marked with this annotation must be 031 * considered by default as {@link Private}.</li> 032 * 033 * <li>External applications must only use classes that are marked 034 * {@link Public}. Avoid using non public classes as these classes 035 * could be removed or change in incompatible ways.</li> 036 * 037 * <li>Hadoop projects must only use classes that are marked 038 * {@link LimitedPrivate} or {@link Public}</li> 039 * 040 * <li> Methods may have a different annotation that it is more restrictive 041 * compared to the audience classification of the class. Example: A class 042 * might be {@link Public}, but a method may be {@link LimitedPrivate} 043 * </li></ul> 044 */ 045@InterfaceAudience.Public 046@InterfaceStability.Evolving 047public class InterfaceAudience { 048 /** 049 * Intended for use by any project or application. 050 */ 051 @Documented 052 @Retention(RetentionPolicy.RUNTIME) 053 public @interface Public {}; 054 055 /** 056 * Intended only for the project(s) specified in the annotation. 057 * For example, "Common", "HDFS", "MapReduce", "ZooKeeper", "HBase". 058 */ 059 @Documented 060 @Retention(RetentionPolicy.RUNTIME) 061 public @interface LimitedPrivate { 062 String[] value(); 063 }; 064 065 /** 066 * Intended for use only within Hadoop itself. 067 */ 068 @Documented 069 @Retention(RetentionPolicy.RUNTIME) 070 public @interface Private {}; 071 072 private InterfaceAudience() {} // Audience can't exist on its own 073}