org.apache.commons.collections4

## Interface OrderedMap<K,V>

- Type Parameters:
    `K` - the type of the keys in the map
    `V` - the type of the values in the map
  All Superinterfaces:
    Get<K,V>, IterableGet<K,V>, IterableMap<K,V>, Map<K,V>, Put<K,V>
  All Known Subinterfaces:
    IterableSortedMap<K,V>, OrderedBidiMap<K,V>, SortedBidiMap<K,V>, Trie<K,V>
  All Known Implementing Classes:
    AbstractBitwiseTrie, AbstractLinkedMap, AbstractOrderedBidiMapDecorator, AbstractOrderedMapDecorator, AbstractSortedBidiMapDecorator, AbstractSortedMapDecorator, DualTreeBidiMap, DualTreeBidiMap.ViewMap, FixedSizeSortedMap, LinkedMap, ListOrderedMap, LRUMap, PatriciaTrie, SingletonMap, TreeBidiMap, UnmodifiableOrderedBidiMap, UnmodifiableOrderedMap, UnmodifiableSortedBidiMap, UnmodifiableSortedMap, UnmodifiableTrie

      public interface OrderedMap<K,V>
      extends IterableMap<K,V>

  Defines a map that maintains order and allows both forward and backward iteration through that order.
  Since:
    3.0
  Version:
    $Id: OrderedMap.java 1543259 2013-11-19 00:47:07Z ggregory $

- - ### Nested Class Summary

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

      `Map.Entry<K,V>`

  - ### Method Summary

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

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

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

    - ### Methods inherited from interface org.apache.commons.collections4.Put

      `clear, put, putAll`

    - ### Methods inherited from interface org.apache.commons.collections4.Get

      `containsKey, containsValue, entrySet, get, isEmpty, keySet, remove, size, values`

- - ### Method Detail

    - #### mapIterator

          OrderedMapIterator<K,V> mapIterator()

      Obtains an `OrderedMapIterator` over the map.

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

      Specified by:
        `mapIterator` in interface `IterableGet<K,V>`
      Returns:
        a map iterator

    - #### firstKey

          K 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

          K 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

          K nextKey(K 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

          K previousKey(K 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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