    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 * </p>
    024 * <pre>
    025 * if (coll instanceof Unmodifiable) {
    026 *   coll = new ArrayList(coll);
    027 * }
    028 * // now we know coll is modifiable
    029 * </pre>
    030 * <p>
    031 * Of course all this only works if you use the Unmodifiable classes defined
    032 * in this library. If you use the JDK unmodifiable class via {@code java.util Collections}
    033 * then the interface won't be there.
    034 * </p>
    035 *
    036 * @since 3.0
    037 */
    038public interface Unmodifiable {
    039    // marker interface - no methods to implement
    040}