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 *      http://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 */
017package org.apache.commons.collections4;
018
019/**
020 * Marker interface for collections, maps and iterators that are unmodifiable.
021 * <p>
022 * This interface enables testing such as:
023 * <pre>
024 * if (coll instanceof Unmodifiable) {
025 *   coll = new ArrayList(coll);
026 * }
027 * // now we know coll is modifiable
028 * </pre>
029 * Of course all this only works if you use the Unmodifiable classes defined
030 * in this library. If you use the JDK unmodifiable class via {@code java.util Collections}
031 * then the interface won't be there.
032 *
033 * @since 3.0
034 */
035public interface Unmodifiable {
036    // marker interface - no methods to implement
037}