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 import java.util.Iterator;
21
22 /**
23 * Defines an iterator that operates over a {@code Map}.
24 * <p>
25 * This iterator is a special version designed for maps. It can be more efficient to use this rather than an entry set iterator where the option is available,
26 * and it is certainly more convenient.
27 * </p>
28 * <p>
29 * A map that provides this interface may not hold the data internally using Map Entry objects, thus this interface can avoid lots of object creation.
30 * </p>
31 * <p>
32 * In use, this iterator iterates through the keys in the map. After each call to {@code next()}, the {@code getValue()} method provides direct access to the
33 * value. The value can also be set using {@code setValue()}.
34 * </p>
35 *
36 * <pre>{@code
37 * MapIterator<String, Integer> it = map.mapIterator();
38 * while (it.hasNext()) {
39 * String key = it.next();
40 * Integer value = it.getValue();
41 * it.setValue(value + 1);
42 * }
43 * }</pre>
44 *
45 * @param <K> The type of the keys in the map.
46 * @param <V> The type of the values in the map.
47 * @since 3.0
48 */
49 public interface MapIterator<K, V> extends Iterator<K> {
50
51 /**
52 * Gets the current key, which is the key returned by the last call to {@code next()}.
53 *
54 * @return The current key.
55 * @throws IllegalStateException if {@code next()} has not yet been called.
56 */
57 K getKey();
58
59 /**
60 * Gets the current value, which is the value associated with the last key returned by {@code next()}.
61 *
62 * @return The current value.
63 * @throws IllegalStateException if {@code next()} has not yet been called.
64 */
65 V getValue();
66
67 /**
68 * Checks to see if there are more entries still to be iterated.
69 *
70 * @return {@code true} if the iterator has more elements
71 */
72 @Override
73 boolean hasNext();
74
75 /**
76 * Gets the next <em>key</em> from the {@code Map}.
77 *
78 * @return The next key in the iteration.
79 * @throws java.util.NoSuchElementException if the iteration is finished.
80 */
81 @Override
82 K next();
83
84 /**
85 * Removes the last returned key from the underlying {@code Map} (optional operation).
86 * <p>
87 * This method can be called once per call to {@code next()}.
88 * </p>
89 *
90 * @throws UnsupportedOperationException if remove is not supported by the map.
91 * @throws IllegalStateException if {@code next()} has not yet been called.
92 * @throws IllegalStateException if {@code remove()} has already been called since the last call to {@code next()}.
93 */
94 @Override
95 void remove();
96
97 /**
98 * Sets the value associated with the current key (optional operation).
99 *
100 * @param value The new value.
101 * @return The previous value.
102 * @throws UnsupportedOperationException if setValue is not supported by the map.
103 * @throws IllegalStateException if {@code next()} has not yet been called.
104 * @throws IllegalStateException if {@code remove()} has been called since the last call to {@code next()}.
105 */
106 V setValue(V value);
107 }