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     */
017    package org.apache.commons.collections;
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 java util Collections
031     * then the interface won't be there.
032     *  
033     * @since Commons Collections 3.0
034     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
035     *
036     * @author Stephen Colebourne
037     */
038    public interface Unmodifiable {
039        // marker interface - no methods to implement
040    }