Package org.apache.commons.collections.map

Class ListOrderedMap

java.lang.Object
org.apache.commons.collections.map.AbstractMapDecorator
org.apache.commons.collections.map.ListOrderedMap
All Implemented Interfaces:
Serializable, Map, IterableMap, OrderedMap
public class ListOrderedMap extends AbstractMapDecorator implements OrderedMap, 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.

This class is Serializable from Commons Collections 3.1.

Since:
Commons Collections 3.0
Version:
$Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
Author:
Henri Yandell, Stephen Colebourne, Matt Benson
See Also:

  • Field Details

    • insertOrder

      protected final List insertOrder
      Internal list to hold the sequence of objects

  • Constructor Details

    • ListOrderedMap

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

    • ListOrderedMap

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

  • Method Details

    • decorate

      public static OrderedMap decorate(Map map)
      Factory method to create an ordered map.

      An ArrayList is used to retain order.

      Parameters:
      map - the map to decorate, must not be null
      Throws:
      IllegalArgumentException - if map is null

    • mapIterator

      public MapIterator mapIterator()
      Description copied from interface: IterableMap
      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 cast to Map Entry objects. 

       IterableMap map = new HashedMap();
 MapIterator it = map.mapIterator();
 while (it.hasNext()) {
   Object key = it.next();
   Object value = it.getValue();
   it.setValue("newValue");
 }
      Specified by:
      mapIterator in interface IterableMap
      Returns:
      a map iterator

    • orderedMapIterator

      public OrderedMapIterator orderedMapIterator()
      Description copied from interface: OrderedMap
      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();
 }
      Specified by:
      orderedMapIterator in interface OrderedMap
      Returns:
      a map iterator

    • firstKey

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

    • lastKey

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

    • nextKey

      public Object 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
      Parameters:
      key - the key to find previous for
      Returns:
      the next key, null if no match or at start

    • previousKey

      public Object 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
      Parameters:
      key - the key to find previous for
      Returns:
      the previous key, null if no match or at start

    • put

      public Object put(Object key, Object value)
      Specified by:
      put in interface Map
      Overrides:
      put in class AbstractMapDecorator

    • putAll

      public void putAll(Map map)
      Specified by:
      putAll in interface Map
      Overrides:
      putAll in class AbstractMapDecorator

    • remove

      public Object remove(Object key)
      Specified by:
      remove in interface Map
      Overrides:
      remove in class AbstractMapDecorator

    • clear

      public void clear()
      Specified by:
      clear in interface Map
      Overrides:
      clear in class AbstractMapDecorator

    • keySet

      public Set 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 Map
      Overrides:
      keySet in class AbstractMapDecorator
      Returns:
      the fully modifiable collection view over the keys
      See Also:

    • keyList

      public List 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:
      Commons Collections 3.2
      See Also:

    • values

      public Collection 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 Map
      Overrides:
      values in class AbstractMapDecorator
      Returns:
      the fully modifiable collection view over the values
      See Also:

    • valueList

      public List 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:
      Commons Collections 3.2
      See Also:

    • entrySet

      public Set 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 Map
      Overrides:
      entrySet in class AbstractMapDecorator
      Returns:
      the fully modifiable set view over the entries

    • toString

      public String toString()
      Returns the Map as a string.
      Overrides:
      toString in class AbstractMapDecorator
      Returns:
      the Map as a String

    • get

      public Object 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 Object 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

    • setValue

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

    • put

      public Object put(int index, Object key, Object 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 ocurred.

      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
      Since:
      Commons Collections 3.2

    • remove

      public Object 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

    • asList

      public List 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: