001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4;
018
019import java.util.Iterator;
020
021/**
022 * Defines an iterator that operates over a {@code Map}.
023 * <p>
024 * This iterator is a special version designed for maps. It can be more
025 * efficient to use this rather than an entry set iterator where the option
026 * is available, and it is certainly more convenient.
027 * </p>
028 * <p>
029 * A map that provides this interface may not hold the data internally using
030 * Map Entry objects, thus this interface can avoid lots of object creation.
031 * </p>
032 * <p>
033 * In use, this iterator iterates through the keys in the map. After each call
034 * to {@code next()}, the {@code getValue()} method provides direct
035 * access to the value. The value can also be set using {@code setValue()}.
036 * </p>
037 * <pre>{@code
038 * MapIterator<String,Integer> it = map.mapIterator();
039 * while (it.hasNext()) {
040 *   String key = it.next();
041 *   Integer value = it.getValue();
042 *   it.setValue(value + 1);
043 * }
044 * }</pre>
045 *
046 * @param <K> the type of the keys in the map
047 * @param <V> the type of the values in the map
048 * @since 3.0
049 */
050public interface MapIterator<K, V> extends Iterator<K> {
051
052    /**
053     * Gets the current key, which is the key returned by the last call
054     * to {@code next()}.
055     *
056     * @return the current key
057     * @throws IllegalStateException if {@code next()} has not yet been called
058     */
059    K getKey();
060
061    /**
062     * Gets the current value, which is the value associated with the last key
063     * returned by {@code next()}.
064     *
065     * @return the current value
066     * @throws IllegalStateException if {@code next()} has not yet been called
067     */
068    V getValue();
069
070    /**
071     * Checks to see if there are more entries still to be iterated.
072     *
073     * @return {@code true} if the iterator has more elements
074     */
075    @Override
076    boolean hasNext();
077
078    /**
079     * Gets the next <em>key</em> from the {@code Map}.
080     *
081     * @return the next key in the iteration
082     * @throws java.util.NoSuchElementException if the iteration is finished
083     */
084    @Override
085    K next();
086
087    /**
088     * Removes the last returned key from the underlying {@code Map} (optional operation).
089     * <p>
090     * This method can be called once per call to {@code next()}.
091     *
092     * @throws UnsupportedOperationException if remove is not supported by the map
093     * @throws IllegalStateException if {@code next()} has not yet been called
094     * @throws IllegalStateException if {@code remove()} has already been called
095     *  since the last call to {@code next()}
096     */
097    @Override
098    void remove();
099
100    /**
101     * Sets the value associated with the current key (optional operation).
102     *
103     * @param value  the new value
104     * @return the previous value
105     * @throws UnsupportedOperationException if setValue is not supported by the map
106     * @throws IllegalStateException if {@code next()} has not yet been called
107     * @throws IllegalStateException if {@code remove()} has been called since the
108     *  last call to {@code next()}
109     */
110    V setValue(V value);
111
112}