org.apache.commons.collections.map

Class LinkedMap

java.lang.Object

java.util.AbstractMap

org.apache.commons.collections.map.AbstractHashedMap

org.apache.commons.collections.map.AbstractLinkedMap

org.apache.commons.collections.map.LinkedMap

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, java.util.Map, IterableMap, OrderedMap

public class LinkedMap
extends AbstractLinkedMap
implements java.io.Serializable, java.lang.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 Collections.synchronizedMap(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.

Since:

Commons Collections 3.0

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class java.util.AbstractMap

java.util.AbstractMap.SimpleEntry<K,V>, java.util.AbstractMap.SimpleImmutableEntry<K,V>

Nested classes/interfaces inherited from interface java.util.Map

java.util.Map.Entry<K,V>

Constructor Summary

Constructors

Constructor and Description
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(java.util.Map map) Constructor copying elements from another map.

Method Summary

Modifier and Type	Method and Description
java.util.List	asList() Gets an unmodifiable List view of the keys.
java.lang.Object	clone() Clones the map without cloning the keys or values.
java.lang.Object	get(int index) Gets the key at the specified index.
java.lang.Object	getValue(int index) Gets the value at the specified index.
int	indexOf(java.lang.Object key) Gets the index of the specified key.
java.lang.Object	remove(int index) Removes the element at the specified index.

Methods inherited from class org.apache.commons.collections.map.AbstractLinkedMap

clear, containsValue, firstKey, lastKey, mapIterator, nextKey, orderedMapIterator, previousKey

Methods inherited from class org.apache.commons.collections.map.AbstractHashedMap

containsKey, entrySet, equals, get, hashCode, isEmpty, keySet, put, putAll, remove, size, toString, values

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map

compute, computeIfAbsent, computeIfPresent, containsKey, entrySet, equals, forEach, get, getOrDefault, hashCode, isEmpty, keySet, merge, put, putAll, putIfAbsent, remove, remove, replace, replace, replaceAll, size, values

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:

java.lang.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:

java.lang.IllegalArgumentException - if the initial capacity is less than one

java.lang.IllegalArgumentException - if the load factor is less than zero

LinkedMap

public LinkedMap(java.util.Map map)

Constructor copying elements from another map.

Parameters:

map - the map to copy

Throws:

java.lang.NullPointerException - if the map is null

Method Detail

clone

public java.lang.Object clone()

Clones the map without cloning the keys or values.

Returns:

a shallow clone

get

public java.lang.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:

java.lang.IndexOutOfBoundsException - if the index is invalid

getValue

public java.lang.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:

java.lang.IndexOutOfBoundsException - if the index is invalid

indexOf

public int indexOf(java.lang.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 java.lang.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:

java.lang.IndexOutOfBoundsException - if the index is invalid

asList

public java.util.List asList()

Gets an unmodifiable List view of the keys.

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 AbstractHashedMap.keySet().

Returns:

The ordered list of keys.

See Also:

AbstractHashedMap.keySet()