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
019/**
020 * Defines a map that maintains order and allows both forward and backward
021 * iteration through that order.
022 *
023 * @param <K> the type of the keys in the map
024 * @param <V> the type of the values in the map
025 * @since 3.0
026 */
027public interface OrderedMap<K, V> extends IterableMap<K, V> {
028
029    /**
030     * Gets the first key currently in this map.
031     *
032     * @return the first key currently in this map
033     * @throws java.util.NoSuchElementException if this map is empty
034     */
035    K firstKey();
036
037    /**
038     * Gets the last key currently in this map.
039     *
040     * @return the last key currently in this map
041     * @throws java.util.NoSuchElementException if this map is empty
042     */
043    K lastKey();
044
045    /**
046     * Obtains an {@code OrderedMapIterator} over the map.
047     * <p>
048     * An ordered map iterator is an efficient way of iterating over maps
049     * in both directions.
050     * </p>
051     *
052     * @return a map iterator
053     */
054    @Override
055    OrderedMapIterator<K, V> mapIterator();
056
057    /**
058     * Gets the next key after the one specified.
059     *
060     * @param key  the key to search for next from
061     * @return the next key, null if no match or at end
062     */
063    K nextKey(K key);
064
065    /**
066     * Gets the previous key before the one specified.
067     *
068     * @param key  the key to search for previous from
069     * @return the previous key, null if no match or at start
070     */
071    K previousKey(K key);
072
073}