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 }