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;
020
021/**
022 * This interface allows legacy classes to be injected by
023 * ConfigurationBuilderImpl. To be of any use, implementations of this class
024 * must have at least one constructor with an @Inject annotation. From
025 * ConfigurationBuilderImpl's perspective, an ExternalConstructor class is just
026 * a special instance of the class T, except that, after injection an
027 * ExternalConstructor, ConfigurationBuilderImpl will call newInstance, and
028 * store the resulting object. It will then discard the ExternalConstructor.
029 *
030 * @param <T> The type this ExternalConstructor will create.
031 */
032public interface ExternalConstructor<T> {
033  /**
034   * This method will only be called once.
035   *
036   * @return a new, distinct instance of T.
037   */
038  T newInstance();
039}