Package org.apache.commons.collections4.map

Class ListOrderedMap<K,V>

java.lang.Object
org.apache.commons.collections4.map.AbstractIterableMap<K,V>
org.apache.commons.collections4.map.AbstractMapDecorator<K,V>
org.apache.commons.collections4.map.ListOrderedMap<K,V>
Type Parameters:
K - the type of the keys in this map
V - the type of the values in this map
All Implemented Interfaces:
Serializable, Map<K,V>, Get<K,V>, IterableGet<K,V>, IterableMap<K,V>, OrderedMap<K,V>, Put<K,V>
public class ListOrderedMap<K,V> extends AbstractMapDecorator<K,V> implements OrderedMap<K,V>, Serializable
Decorates a Map to ensure that the order of addition is retained using a List to maintain order.

The order will be used via the iterators and toArray methods on the views. The order is also returned by the MapIterator. The orderedMapIterator() method accesses an iterator that can iterate both forwards and backwards through the map. In addition, non-interface methods are provided to access the map by index.

If an object is added to the Map for a second time, it will remain in the original position in the iteration.

Note that ListOrderedMap is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. The simplest approach is to wrap this map using Collections.synchronizedMap(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.

Note that ListOrderedMap doesn't work with IdentityHashMap, CaseInsensitiveMap, or similar maps that violate the general contract of Map. The ListOrderedMap (or, more precisely, the underlying List) is relying on equals(). This is fine, as long as the decorated Map is also based on equals(), and hashCode(), which IdentityHashMap, and CaseInsensitiveMap don't: The former uses ==, and the latter uses equals() on a lower-cased key.

This class is Serializable starting with Commons Collections 3.1.

Since:
3.0
See Also:

  • Constructor Details

    • ListOrderedMap

      public ListOrderedMap()
      Constructs a new empty ListOrderedMap that decorates a HashMap.
      Since:
      3.1

    • ListOrderedMap

      protected ListOrderedMap(Map<K,V> map)
      Constructor that wraps (not copies).
      Parameters:
      map - the map to decorate, must not be null
      Throws:
      NullPointerException - if map is null

  • Method Details

    • listOrderedMap

      public static <K, V> ListOrderedMap<K,V> listOrderedMap(Map<K,V> map)
      Factory method to create an ordered map.

      An ArrayList is used to retain order.

      Type Parameters:
      K - the key type
      V - the value type
      Parameters:
      map - the map to decorate, must not be null
      Returns:
      a new list ordered map
      Throws:
      NullPointerException - if map is null
      Since:
      4.0

    • asList

      public List<K> asList()
      Gets an unmodifiable List view of the keys which changes as the map changes.

      The returned list is unmodifiable because changes to the values of the list (using ListIterator.set(Object)) will effectively remove the value from the list and reinsert that value at the end of the list, which is an unexpected side effect of changing the value of a list. This occurs because changing the key, changes when the mapping is added to the map and thus where it appears in the list.

      An alternative to this method is to use the better named keyList() or keySet().

      Returns:
      The ordered list of keys.
      See Also:

    • clear

      public void clear()
      Specified by:
      clear in interface Map<K,V>
      Specified by:
      clear in interface Put<K,V>
      Overrides:
      clear in class AbstractMapDecorator<K,V>
      See Also:

    • entrySet

      public Set<Map.Entry<K,V>> entrySet()
      Gets a view over the entries in the map.

      The Set will be ordered by object insertion into the map.

      Specified by:
      entrySet in interface Get<K,V>
      Specified by:
      entrySet in interface Map<K,V>
      Overrides:
      entrySet in class AbstractMapDecorator<K,V>
      Returns:
      the fully modifiable set view over the entries
      See Also:

    • firstKey

      public K firstKey()
      Gets the first key in this map by insert order.
      Specified by:
      firstKey in interface OrderedMap<K,V>
      Returns:
      the first key currently in this map
      Throws:
      NoSuchElementException - if this map is empty

    • get

      public K get(int index)
      Gets the key at the specified index.
      Parameters:
      index - the index to retrieve
      Returns:
      the key at the specified index
      Throws:
      IndexOutOfBoundsException - if the index is invalid

    • getValue

      public V getValue(int index)
      Gets the value at the specified index.
      Parameters:
      index - the index to retrieve
      Returns:
      the key at the specified index
      Throws:
      IndexOutOfBoundsException - if the index is invalid

    • indexOf

      public int indexOf(Object key)
      Gets the index of the specified key.
      Parameters:
      key - the key to find the index of
      Returns:
      the index, or -1 if not found

    • keyList

      public List<K> keyList()
      Gets a view over the keys in the map as a List.

      The List will be ordered by object insertion into the map. The List is unmodifiable.

      Returns:
      the unmodifiable list view over the keys
      Since:
      3.2
      See Also:

    • keySet

      public Set<K> keySet()
      Gets a view over the keys in the map.

      The Collection will be ordered by object insertion into the map.

      Specified by:
      keySet in interface Get<K,V>
      Specified by:
      keySet in interface Map<K,V>
      Overrides:
      keySet in class AbstractMapDecorator<K,V>
      Returns:
      the fully modifiable collection view over the keys
      See Also:

    • lastKey

      public K lastKey()
      Gets the last key in this map by insert order.
      Specified by:
      lastKey in interface OrderedMap<K,V>
      Returns:
      the last key currently in this map
      Throws:
      NoSuchElementException - if this map is empty

    • mapIterator

      public OrderedMapIterator<K,V> mapIterator()
      Description copied from class: AbstractIterableMap
      Obtains a MapIterator over the map.

      A map iterator is an efficient way of iterating over maps. There is no need to access the entry set or use Map Entry objects. 

       IterableMap<String,Integer> map = new HashedMap<String,Integer>();
 MapIterator<String,Integer> it = map.mapIterator();
 while (it.hasNext()) {
   String key = it.next();
   Integer value = it.getValue();
   it.setValue(value + 1);
 }
      Specified by:
      mapIterator in interface IterableGet<K,V>
      Specified by:
      mapIterator in interface OrderedMap<K,V>
      Overrides:
      mapIterator in class AbstractIterableMap<K,V>
      Returns:
      a map iterator

    • nextKey

      public K nextKey(Object key)
      Gets the next key to the one specified using insert order. This method performs a list search to find the key and is O(n).
      Specified by:
      nextKey in interface OrderedMap<K,V>
      Parameters:
      key - the key to find previous for
      Returns:
      the next key, null if no match or at start

    • previousKey

      public K previousKey(Object key)
      Gets the previous key to the one specified using insert order. This method performs a list search to find the key and is O(n).
      Specified by:
      previousKey in interface OrderedMap<K,V>
      Parameters:
      key - the key to find previous for
      Returns:
      the previous key, null if no match or at start

    • put

      public V put(int index, K key, V value)
      Puts a key-value mapping into the map at the specified index.

      If the map already contains the key, then the original mapping is removed and the new mapping added at the specified index. The remove may change the effect of the index. The index is always calculated relative to the original state of the map.

      Thus, the steps are: (1) remove the existing key-value mapping, then (2) insert the new key-value mapping at the position it would have been inserted had the remove not occurred.

      Parameters:
      index - the index at which the mapping should be inserted
      key - the key
      value - the value
      Returns:
      the value previously mapped to the key
      Throws:
      IndexOutOfBoundsException - if the index is out of range [0, size]
      Since:
      3.2

    • put

      public V put(K key, V value)
      Description copied from interface: Put
      Note that the return type is Object, rather than V as in the Map interface. See the class Javadoc for further info.
      Specified by:
      put in interface Map<K,V>
      Specified by:
      put in interface Put<K,V>
      Overrides:
      put in class AbstractMapDecorator<K,V>
      Parameters:
      key - key with which the specified value is to be associated
      value - value to be associated with the specified key
      Returns:
      the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with key, if the implementation supports null values.)
      See Also:

    • putAll

      public void putAll(int index, Map<? extends K,? extends V> map)
      Puts the values contained in a supplied Map into the Map starting at the specified index.
      Parameters:
      index - the index in the Map to start at.
      map - the Map containing the entries to be added.
      Throws:
      IndexOutOfBoundsException - if the index is out of range [0, size]

    • putAll

      public void putAll(Map<? extends K,? extends V> map)
      Specified by:
      putAll in interface Map<K,V>
      Specified by:
      putAll in interface Put<K,V>
      Overrides:
      putAll in class AbstractMapDecorator<K,V>
      Parameters:
      map - mappings to be stored in this map
      See Also:

    • remove

      public V remove(int index)
      Removes the element at the specified index.
      Parameters:
      index - the index of the object to remove
      Returns:
      the removed value, or null if none existed
      Throws:
      IndexOutOfBoundsException - if the index is invalid

    • remove

      public V remove(Object key)
      Specified by:
      remove in interface Get<K,V>
      Specified by:
      remove in interface Map<K,V>
      Overrides:
      remove in class AbstractMapDecorator<K,V>
      Parameters:
      key - key whose mapping is to be removed from the map
      Returns:
      the previous value associated with key, or null if there was no mapping for key.
      See Also:

    • setValue

      public V setValue(int index, V value)
      Sets the value at the specified index.
      Parameters:
      index - the index of the value to set
      value - the new value to set
      Returns:
      the previous value at that index
      Throws:
      IndexOutOfBoundsException - if the index is invalid
      Since:
      3.2

    • toString

      public String toString()
      Returns the Map as a string.
      Overrides:
      toString in class AbstractMapDecorator<K,V>
      Returns:
      the Map as a String

    • valueList

      public List<V> valueList()
      Gets a view over the values in the map as a List.

      The List will be ordered by object insertion into the map. The List supports remove and set, but does not support add.

      Returns:
      the partially modifiable list view over the values
      Since:
      3.2
      See Also:

    • values

      public Collection<V> values()
      Gets a view over the values in the map.

      The Collection will be ordered by object insertion into the map.

      From Commons Collections 3.2, this Collection can be cast to a list, see valueList()

      Specified by:
      values in interface Get<K,V>
      Specified by:
      values in interface Map<K,V>
      Overrides:
      values in class AbstractMapDecorator<K,V>
      Returns:
      the fully modifiable collection view over the values
      See Also: