org.apache.commons.collections.map

Class LinkedMap

public class LinkedMap extends AbstractLinkedMap implements Serializable, Cloneable

A Map implementation that maintains the order of the entries. In this implementation order is maintained by original insertion.

This implementation improves on the JDK1.4 LinkedHashMap by adding the MapIterator functionality, additional convenience methods and allowing bidirectional iteration. It also implements OrderedMap. In addition, non-interface methods are provided to access the map by index.

The orderedMapIterator() method provides direct access to a bidirectional iterator. The iterators from the other views can also be cast to OrderedIterator if required.

All the available iterators can be reset back to the start by casting to ResettableIterator and calling reset().

The implementation is also designed to be subclassed, with lots of useful methods exposed.

Note that LinkedMap 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.

Since: Commons Collections 3.0

Version: $Revision: 348007 $ $Date: 2005-11-21 22:52:57 +0000 (Mon, 21 Nov 2005) $

Author: Stephen Colebourne

Constructor Summary
LinkedMap()
Constructs a new empty map with default size and load factor.
LinkedMap(int initialCapacity)
Constructs a new, empty map with the specified initial capacity.
LinkedMap(int initialCapacity, float loadFactor)
Constructs a new, empty map with the specified initial capacity and load factor.
LinkedMap(Map map)
Constructor copying elements from another map.
Method Summary
ListasList()
Gets an unmodifiable List view of the keys.
Objectclone()
Clones the map without cloning the keys or values.
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.
Objectremove(int index)
Removes the element at the specified index.

Constructor Detail

LinkedMap

public LinkedMap()
Constructs a new empty map with default size and load factor.

LinkedMap

public LinkedMap(int initialCapacity)
Constructs a new, empty map with the specified initial capacity.

Parameters: initialCapacity the initial capacity

Throws: IllegalArgumentException if the initial capacity is less than one

LinkedMap

public LinkedMap(int initialCapacity, float loadFactor)
Constructs a new, empty map with the specified initial capacity and load factor.

Parameters: initialCapacity the initial capacity loadFactor the load factor

Throws: IllegalArgumentException if the initial capacity is less than one IllegalArgumentException if the load factor is less than zero

LinkedMap

public LinkedMap(Map map)
Constructor copying elements from another map.

Parameters: map the map to copy

Throws: NullPointerException if the map is null

Method Detail

asList

public List asList()
Gets an unmodifiable List view of the keys.

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 LinkedMap.

Returns: The ordered list of keys.

See Also: LinkedMap

clone

public Object clone()
Clones the map without cloning the keys or values.

Returns: a shallow clone

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

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

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