    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 *      https://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 */
    017
    018package org.apache.commons.collections4;
    019
    020import java.util.Iterator;
    021
    022/**
    023 * Defines an iterator that operates over a {@code Map}.
    024 * <p>
    025 * 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,
    026 * and it is certainly more convenient.
    027 * </p>
    028 * <p>
    029 * 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.
    030 * </p>
    031 * <p>
    032 * 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
    033 * value. The value can also be set using {@code setValue()}.
    034 * </p>
    035 *
    036 * <pre>{@code
    037 * MapIterator<String, Integer> it = map.mapIterator();
    038 * while (it.hasNext()) {
    039 *     String key = it.next();
    040 *     Integer value = it.getValue();
    041 *     it.setValue(value + 1);
    042 * }
    043 * }</pre>
    044 *
    045 * @param <K> The type of the keys in the map.
    046 * @param <V> The type of the values in the map.
    047 * @since 3.0
    048 */
    049public interface MapIterator<K, V> extends Iterator<K> {
    050
    051    /**
    052     * Gets the current key, which is the key returned by the last call to {@code next()}.
    053     *
    054     * @return The current key.
    055     * @throws IllegalStateException if {@code next()} has not yet been called.
    056     */
    057    K getKey();
    058
    059    /**
    060     * Gets the current value, which is the value associated with the last key returned by {@code next()}.
    061     *
    062     * @return The current value.
    063     * @throws IllegalStateException if {@code next()} has not yet been called.
    064     */
    065    V getValue();
    066
    067    /**
    068     * Checks to see if there are more entries still to be iterated.
    069     *
    070     * @return {@code true} if the iterator has more elements
    071     */
    072    @Override
    073    boolean hasNext();
    074
    075    /**
    076     * Gets the next <em>key</em> from the {@code Map}.
    077     *
    078     * @return The next key in the iteration.
    079     * @throws java.util.NoSuchElementException if the iteration is finished.
    080     */
    081    @Override
    082    K next();
    083
    084    /**
    085     * Removes the last returned key from the underlying {@code Map} (optional operation).
    086     * <p>
    087     * This method can be called once per call to {@code next()}.
    088     * </p>
    089     *
    090     * @throws UnsupportedOperationException if remove is not supported by the map.
    091     * @throws IllegalStateException         if {@code next()} has not yet been called.
    092     * @throws IllegalStateException         if {@code remove()} has already been called since the last call to {@code next()}.
    093     */
    094    @Override
    095    void remove();
    096
    097    /**
    098     * Sets the value associated with the current key (optional operation).
    099     *
    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}