Source code

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,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.reef.tang.annotations;
020
021import java.lang.annotation.ElementType;
022import java.lang.annotation.Retention;
023import java.lang.annotation.RetentionPolicy;
024import java.lang.annotation.Target;
025
026/**
027 * A TANG Unit consists of an outer class and some non-static inner classes.
028 * TANG injectors automatically treat all the classes in a unit as singletons.
029 * <p>
030 * In order to inject the singleton instance of each inner class, TANG first
031 * instantiates the outer class and then uses the resulting instance to
032 * instantiate each inner class.
033 * <p>
034 * Classes annotated in this way must have at least one non-static inner class
035 * and no static inner classes. The inner classes must not declare any
036 * constructors.
037 * <p>
038 * Furthermore, classes annotated with Unit may not have injectable (or Unit)
039 * subclasses.
040 */
041@Target(ElementType.TYPE)
042@Retention(RetentionPolicy.RUNTIME)
043public @interface Unit {
044
045}