1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * https://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18 package org.apache.commons.collections4;
19
20 /**
21 * Marker interface for collections, maps and iterators that are unmodifiable.
22 * <p>
23 * This interface enables testing such as:
24 * </p>
25 *
26 * <pre>
27 * if (coll instanceof Unmodifiable) {
28 * coll = new ArrayList(coll);
29 * }
30 * // now we know coll is modifiable
31 * </pre>
32 * <p>
33 * Of course all this only works if you use the Unmodifiable classes defined in this library. If you use the JDK unmodifiable class via
34 * {@code java.util Collections} then the interface won't be there.
35 * </p>
36 *
37 * @since 3.0
38 */
39 public interface Unmodifiable {
40 // marker interface - no methods to implement.
41 }