org.apache.commons.collections

## Interface OrderedMap

- All Superinterfaces:
    IterableMap, Map
  All Known Subinterfaces:
    OrderedBidiMap, SortedBidiMap
  All Known Implementing Classes:
    AbstractLinkedMap, AbstractOrderedBidiMapDecorator, AbstractOrderedMapDecorator, AbstractSortedBidiMapDecorator, DualTreeBidiMap, LinkedMap, ListOrderedMap, LRUMap, SingletonMap, TreeBidiMap, UnmodifiableOrderedBidiMap, UnmodifiableOrderedMap, UnmodifiableSortedBidiMap

      public interface OrderedMap
      extends IterableMap

  Defines a map that maintains order and allows both forward and backward iteration through that order.
  Since:
    Commons Collections 3.0
  Version:
    $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
  Author:
    Stephen Colebourne

- - ### Nested Class Summary

    - ### Nested classes/interfaces inherited from interface java.util.Map

      `Map.Entry`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `Object` | `firstKey()` Gets the first key currently in this map.
    `Object` | `lastKey()` Gets the last key currently in this map.
    `Object` | `nextKey(Object key)` Gets the next key after the one specified.
    `OrderedMapIterator` | `orderedMapIterator()` Obtains an `OrderedMapIterator` over the map.
    `Object` | `previousKey(Object key)` Gets the previous key before the one specified.

    - ### Methods inherited from interface org.apache.commons.collections.IterableMap

      `mapIterator`

    - ### Methods inherited from interface java.util.Map

      `clear, containsKey, containsValue, entrySet, equals, get, hashCode, isEmpty, keySet, put, putAll, remove, size, values`

- - ### Method Detail

    - #### orderedMapIterator

          OrderedMapIterator orderedMapIterator()

      Obtains an `OrderedMapIterator` over the map.

      A ordered map iterator is an efficient way of iterating over maps in both directions.

           BidiMap map = new TreeBidiMap();
           MapIterator it = map.mapIterator();
           while (it.hasNext()) {
             Object key = it.next();
             Object value = it.getValue();
             it.setValue("newValue");
             Object previousKey = it.previous();
           }

      Returns:
        a map iterator

    - #### firstKey

          Object firstKey()

      Gets the first key currently in this map.
      Returns:
        the first key currently in this map
      Throws:
        `NoSuchElementException` - if this map is empty

    - #### lastKey

          Object lastKey()

      Gets the last key currently in this map.
      Returns:
        the last key currently in this map
      Throws:
        `NoSuchElementException` - if this map is empty

    - #### nextKey

          Object nextKey(Object key)

      Gets the next key after the one specified.
      Parameters:
        `key` - the key to search for next from
      Returns:
        the next key, null if no match or at end

    - #### previousKey

          Object previousKey(Object key)

      Gets the previous key before the one specified.
      Parameters:
        `key` - the key to search for previous from
      Returns:
        the previous key, null if no match or at start

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