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 * http://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 package org.apache.commons.collections4;
18
19 import java.util.List;
20
21 /**
22 * Defines a map that holds a list of values against each key.
23 * <p>
24 * A {@code ListValuedMap} is a Map with slightly different semantics:
25 * </p>
26 * <ul>
27 * <li>Putting a value into the map will add the value to a {@link List} at that key.</li>
28 * <li>Getting a value will return a {@link List}, holding all the values put to that key.</li>
29 * </ul>
30 *
31 * @param <K> the type of the keys in this map
32 * @param <V> the type of the values in this map
33 * @since 4.1
34 */
35 public interface ListValuedMap<K, V> extends MultiValuedMap<K, V> {
36
37 /**
38 * Gets the list of values associated with the specified key.
39 * <p>
40 * This method will return an <b>empty</b> list if
41 * {@link #containsKey(Object)} returns {@code false}. Changes to the
42 * returned list will update the underlying {@code ListValuedMap} and
43 * vice-versa.
44 *
45 * @param key the key to retrieve
46 * @return the {@code List} of values, implementations should return an
47 * empty {@code List} for no mapping
48 * @throws NullPointerException if the key is null and null keys are invalid
49 */
50 @Override
51 List<V> get(K key);
52
53 /**
54 * Removes all values associated with the specified key.
55 * <p>
56 * The returned list <i>may</i> be modifiable, but updates will not be
57 * propagated to this list-valued map. In case no mapping was stored for the
58 * specified key, an empty, unmodifiable list will be returned.
59 *
60 * @param key the key to remove values from
61 * @return the {@code List} of values removed, implementations
62 * typically return an empty, unmodifiable {@code List} for no mapping found
63 * @throws UnsupportedOperationException if the map is unmodifiable
64 * @throws NullPointerException if the key is null and null keys are invalid
65 */
66 @Override
67 List<V> remove(Object key);
68
69 }