001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      https://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018package org.apache.commons.collections4;
019
020/**
021 * Marker interface for collections, maps and iterators that are unmodifiable.
022 * <p>
023 * This interface enables testing such as:
024 * </p>
025 *
026 * <pre>
027 * if (coll instanceof Unmodifiable) {
028 *     coll = new ArrayList(coll);
029 * }
030 * // now we know coll is modifiable
031 * </pre>
032 * <p>
033 * Of course all this only works if you use the Unmodifiable classes defined in this library. If you use the JDK unmodifiable class via
034 * {@code java.util Collections} then the interface won't be there.
035 * </p>
036 *
037 * @since 3.0
038 */
039public interface Unmodifiable {
040    // marker interface - no methods to implement.
041}