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 /**
20 * Defines a map that maintains order and allows both forward and backward
21 * iteration through that order.
22 *
23 * @param <K> the type of the keys in the map
24 * @param <V> the type of the values in the map
25 * @since 3.0
26 */
27 public interface OrderedMap<K, V> extends IterableMap<K, V> {
28
29 /**
30 * Gets the first key currently in this map.
31 *
32 * @return the first key currently in this map
33 * @throws java.util.NoSuchElementException if this map is empty
34 */
35 K firstKey();
36
37 /**
38 * Gets the last key currently in this map.
39 *
40 * @return the last key currently in this map
41 * @throws java.util.NoSuchElementException if this map is empty
42 */
43 K lastKey();
44
45 /**
46 * Obtains an {@code OrderedMapIterator} over the map.
47 * <p>
48 * An ordered map iterator is an efficient way of iterating over maps
49 * in both directions.
50 * </p>
51 *
52 * @return a map iterator
53 */
54 @Override
55 OrderedMapIterator<K, V> mapIterator();
56
57 /**
58 * Gets the next key after the one specified.
59 *
60 * @param key the key to search for next from
61 * @return the next key, null if no match or at end
62 */
63 K nextKey(K key);
64
65 /**
66 * Gets the previous key before the one specified.
67 *
68 * @param key the key to search for previous from
69 * @return the previous key, null if no match or at start
70 */
71 K previousKey(K key);
72
73 }