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.

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 java.util.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: 365406 $ $Date: 2006-01-02 19:34:53 +0000 (Mon, 02 Jan 2006) $

Author: Henri Yandell Stephen Colebourne Matt Benson

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()
Gets a view over the entries in the map.
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.
ListkeyList()
Gets a view over the keys in the map as a List.
SetkeySet()
Gets a view over the keys in the map.
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)
Objectput(int index, Object key, Object value)
Puts a key-value mapping into the map at the specified index.
voidputAll(Map map)
Objectremove(Object key)
Objectremove(int index)
Removes the element at the specified index.
ObjectsetValue(int index, Object value)
Sets the value at the specified index.
StringtoString()
Returns the Map as a string.
ListvalueList()
Gets a view over the values in the map as a List.
Collectionvalues()
Gets a view over the values in the map.

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 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 the better named keyList or keySet.

Returns: The ordered list of keys.

See Also: keyList 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()
Gets a view over the entries in the map.

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

Returns: the fully modifiable set view over the entries

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

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: keySet

keySet

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

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

Returns: the fully modifiable collection view over the keys

See Also: keyList

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)

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

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 removed value, or null if none existed

Throws: IndexOutOfBoundsException if the index is invalid

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

toString

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

Returns: the Map as a String

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: values

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

Returns: the fully modifiable collection view over the values

See Also: valueList

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