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 */
017 package org.apache.commons.collections;
018
019 /**
020 * Defines a map that maintains order and allows both forward and backward
021 * iteration through that order.
022 *
023 * @since Commons Collections 3.0
024 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
025 *
026 * @author Stephen Colebourne
027 */
028 public interface OrderedMap extends IterableMap {
029
030 /**
031 * Obtains an <code>OrderedMapIterator</code> over the map.
032 * <p>
033 * A ordered map iterator is an efficient way of iterating over maps
034 * in both directions.
035 * <pre>
036 * BidiMap map = new TreeBidiMap();
037 * MapIterator it = map.mapIterator();
038 * while (it.hasNext()) {
039 * Object key = it.next();
040 * Object value = it.getValue();
041 * it.setValue("newValue");
042 * Object previousKey = it.previous();
043 * }
044 * </pre>
045 *
046 * @return a map iterator
047 */
048 OrderedMapIterator orderedMapIterator();
049
050 /**
051 * Gets the first key currently in this map.
052 *
053 * @return the first key currently in this map
054 * @throws java.util.NoSuchElementException if this map is empty
055 */
056 public Object firstKey();
057
058 /**
059 * Gets the last key currently in this map.
060 *
061 * @return the last key currently in this map
062 * @throws java.util.NoSuchElementException if this map is empty
063 */
064 public Object lastKey();
065
066 /**
067 * Gets the next key after the one specified.
068 *
069 * @param key the key to search for next from
070 * @return the next key, null if no match or at end
071 */
072 public Object nextKey(Object key);
073
074 /**
075 * Gets the previous key before the one specified.
076 *
077 * @param key the key to search for previous from
078 * @return the previous key, null if no match or at start
079 */
080 public Object previousKey(Object key);
081
082 }