Package org.apache.commons.collections4.map

Class LinkedMap<K,V>

java.lang.Object
java.util.AbstractMap<K,V>
org.apache.commons.collections4.map.AbstractHashedMap<K,V>
org.apache.commons.collections4.map.AbstractLinkedMap<K,V>
org.apache.commons.collections4.map.LinkedMap<K,V>
Type Parameters:
K - the type of the keys in this map
V - the type of the values in this map
All Implemented Interfaces:
Serializable, Cloneable, Map<K,V>, Get<K,V>, IterableGet<K,V>, IterableMap<K,V>, OrderedMap<K,V>, Put<K,V>
public class LinkedMap<K,V> extends AbstractLinkedMap<K,V> 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 Collections.synchronizedMap(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.

Since:
3.0
See Also:

  • Constructor Details

    • 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 negative

    • 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 negative
      IllegalArgumentException - if the load factor is less than zero

    • LinkedMap

      public LinkedMap(Map<? extends K,? extends V> map)
      Constructor copying elements from another map.
      Parameters:
      map - the map to copy
      Throws:
      NullPointerException - if the map is null

  • Method Details

    • asList

      public List<K> 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:

    • clone

      public LinkedMap<K,V> clone()
      Clones the map without cloning the keys or values.
      Overrides:
      clone in class AbstractHashedMap<K,V>
      Returns:
      a shallow clone

    • get

      public K 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 V getValue(int index)
      Gets the value at the specified index.
      Parameters:
      index - the index to retrieve
      Returns:
      the value 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 V 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