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.Set;
20
21 /**
22 * Defines a map that holds a set of values against each key.
23 * <p>
24 * A {@code SetValuedMap} 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 Set} at that key.</li>
28 * <li>Getting a value will return a {@link Set}, 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 SetValuedMap<K, V> extends MultiValuedMap<K, V> {
36
37 /**
38 * Gets the set of values associated with the specified key.
39 * <p>
40 * Implementations typically return an empty {@code Set} if no values
41 * have been mapped to the key.
42 * </p>
43 *
44 * @param key the key to retrieve
45 * @return the {@code Set} of values, implementations should return an
46 * empty {@code Set} for no mapping
47 * @throws NullPointerException if the key is null and null keys are invalid
48 */
49 @Override
50 Set<V> get(K key);
51
52 /**
53 * Removes all values associated with the specified key.
54 * <p>
55 * The returned set <em>may</em> be modifiable, but updates will not be
56 * propagated to this set-valued map. In case no mapping was stored for the
57 * specified key, an empty, unmodifiable set will be returned.
58 * </p>
59 *
60 * @param key the key to remove values from
61 * @return the {@code Set} of values removed, implementations should
62 * return null for no mapping found, but may return an empty collection
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 Set<V> remove(Object key);
68 }