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.collections;
18
19 import java.util.Iterator;
20
21 /**
22 * Defines an iterator that operates over a <code>Map</code>.
23 * <p>
24 * This iterator is a special version designed for maps. It can be more
25 * efficient to use this rather than an entry set iterator where the option
26 * is available, and it is certainly more convenient.
27 * <p>
28 * A map that provides this interface may not hold the data internally using
29 * Map Entry objects, thus this interface can avoid lots of object creation.
30 * <p>
31 * In use, this iterator iterates through the keys in the map. After each call
32 * to <code>next()</code>, the <code>getValue()</code> method provides direct
33 * access to the value. The value can also be set using <code>setValue()</code>.
34 * <pre>
35 * MapIterator<String,Integer> it = map.mapIterator();
36 * while (it.hasNext()) {
37 * String key = it.next();
38 * Integer value = it.getValue();
39 * it.setValue(value + 1);
40 * }
41 * </pre>
42 *
43 * @param <K> the type of the keys in the map
44 * @param <V> the type of the values in the map
45 * @since 3.0
46 * @version $Id: MapIterator.java 1361710 2012-07-15 15:00:21Z tn $
47 */
48 public interface MapIterator<K, V> extends Iterator<K> {
49
50 /**
51 * Checks to see if there are more entries still to be iterated.
52 *
53 * @return <code>true</code> if the iterator has more elements
54 */
55 boolean hasNext();
56
57 /**
58 * Gets the next <em>key</em> from the <code>Map</code>.
59 *
60 * @return the next key in the iteration
61 * @throws java.util.NoSuchElementException if the iteration is finished
62 */
63 K next();
64
65 //-----------------------------------------------------------------------
66 /**
67 * Gets the current key, which is the key returned by the last call
68 * to <code>next()</code>.
69 *
70 * @return the current key
71 * @throws IllegalStateException if <code>next()</code> has not yet been called
72 */
73 K getKey();
74
75 /**
76 * Gets the current value, which is the value associated with the last key
77 * returned by <code>next()</code>.
78 *
79 * @return the current value
80 * @throws IllegalStateException if <code>next()</code> has not yet been called
81 */
82 V getValue();
83
84 //-----------------------------------------------------------------------
85 /**
86 * Removes the last returned key from the underlying <code>Map</code> (optional operation).
87 * <p>
88 * This method can be called once per call to <code>next()</code>.
89 *
90 * @throws UnsupportedOperationException if remove is not supported by the map
91 * @throws IllegalStateException if <code>next()</code> has not yet been called
92 * @throws IllegalStateException if <code>remove()</code> has already been called
93 * since the last call to <code>next()</code>
94 */
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()</code> has not yet been called
104 * @throws IllegalStateException if <code>remove()</code> has been called since the
105 * last call to <code>next()</code>
106 */
107 V setValue(V value);
108
109 }