org.apache.commons.collections.map

Class ListOrderedMap

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.

This class is Serializable from Commons Collections 3.1.

Since: Commons Collections 3.0

Version: $Revision: 1.16 $ $Date: 2004/06/07 21:51:39 $

Author: Henri Yandell Stephen Colebourne

Field Summary
protected ListinsertOrder
Internal list to hold the sequence of objects
Constructor Summary
ListOrderedMap()
Constructs a new empty ListOrderedMap that decorates a HashMap.
protected ListOrderedMap(Map map)
Constructor that wraps (not copies).
Method Summary
ListasList()
Gets an unmodifiable List view of the keys which changes as the map changes.
voidclear()
static OrderedMapdecorate(Map map)
Factory method to create an ordered map.
SetentrySet()
ObjectfirstKey()
Gets the first key in this map by insert order.
Objectget(int index)
Gets the key at the specified index.
ObjectgetValue(int index)
Gets the value at the specified index.
intindexOf(Object key)
Gets the index of the specified key.
SetkeySet()
ObjectlastKey()
Gets the last key in this map by insert order.
MapIteratormapIterator()
ObjectnextKey(Object key)
Gets the next key to the one specified using insert order.
OrderedMapIteratororderedMapIterator()
ObjectpreviousKey(Object key)
Gets the previous key to the one specified using insert order.
Objectput(Object key, Object value)
voidputAll(Map map)
Objectremove(Object key)
Objectremove(int index)
Removes the element at the specified index.
StringtoString()
Returns the Map as a string.
Collectionvalues()

Field Detail

insertOrder

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

Constructor Detail

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 Detail

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 {@link java.util.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 {@link #keySet()}.

Returns: The ordered list of keys.

See Also: keySet

clear

public void clear()

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

entrySet

public Set entrySet()

firstKey

public Object firstKey()
Gets the first key in this map by insert order.

Returns: the first key currently in this map

Throws: NoSuchElementException if this map is empty

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

keySet

public Set keySet()

lastKey

public Object lastKey()
Gets the last key in this map by insert order.

Returns: the last key currently in this map

Throws: NoSuchElementException if this map is empty

mapIterator

public MapIterator mapIterator()

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).

Parameters: key the key to find previous for

Returns: the next key, null if no match or at start

orderedMapIterator

public OrderedMapIterator orderedMapIterator()

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).

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)

putAll

public void putAll(Map map)

remove

public Object remove(Object key)

remove

public Object remove(int index)
Removes the element at the specified index.

Parameters: index the index of the object to remove

Returns: the previous value corresponding the key, or null if none existed

Throws: IndexOutOfBoundsException if the index is invalid

toString

public String toString()
Returns the Map as a string.

Returns: the Map as a String

values

public Collection values()
Copyright © 2001-2008 Apache Software Foundation. All Rights Reserved.