## org.apache.commons.collections.map
Class AbstractLinkedMap

    java.lang.Object
      java.util.AbstractMap
          org.apache.commons.collections.map.AbstractHashedMap
              org.apache.commons.collections.map.AbstractLinkedMap

All Implemented Interfaces:
  IterableMap, Map, OrderedMap

Direct Known Subclasses:
  LinkedMap, LRUMap

public class AbstractLinkedMap
extends AbstractHashedMap
implements OrderedMap

An abstract implementation of a hash-based map that links entries to create an ordered map and which provides numerous points for subclasses to override.

This class implements all the features necessary for a subclass linked hash-based map. Key-value entries are stored in instances of the `LinkEntry` class which can be overridden and replaced. The iterators can similarly be replaced, without the need to replace the KeySet, EntrySet and Values view classes.

Overridable methods are provided to change the default hashing behaviour, and to change how entries are added to and removed from the map. Hopefully, all you need for unusual subclasses is here.

This implementation maintains order by original insertion, but subclasses may work differently. The `OrderedMap` interface is implemented to provide access to bidirectional iteration and extra convenience methods.

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.

Since:
  Commons Collections 3.0
Version:
  $Revision: 1.12 $ $Date: 2004/05/26 21:56:05 $
Author:
  java util LinkedHashMap, Stephen Colebourne

Nested Class Summary
`protected static class` `AbstractLinkedMap.EntrySetIterator` EntrySet iterator.
`protected static class` `AbstractLinkedMap.KeySetIterator` KeySet iterator.
`protected static class` `AbstractLinkedMap.LinkEntry` LinkEntry that stores the data.
`protected static class` `AbstractLinkedMap.LinkIterator` Base Iterator that iterates in link order.
`protected static class` `AbstractLinkedMap.LinkMapIterator` MapIterator implementation.
`protected static class` `AbstractLinkedMap.ValuesIterator` Values iterator.

Nested classes inherited from class org.apache.commons.collections.map.AbstractHashedMap
`AbstractHashedMap.EntrySet, AbstractHashedMap.HashEntry, AbstractHashedMap.HashIterator, AbstractHashedMap.HashMapIterator, AbstractHashedMap.KeySet, AbstractHashedMap.Values`

Nested classes inherited from class java.util.Map
`Map.Entry`

Field Summary
`protected AbstractLinkedMap.LinkEntry` `header` Header in the linked list

Fields inherited from class org.apache.commons.collections.map.AbstractHashedMap
`data, DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_THRESHOLD, entrySet, GETKEY_INVALID, GETVALUE_INVALID, keySet, loadFactor, MAXIMUM_CAPACITY, modCount, NO_NEXT_ENTRY, NO_PREVIOUS_ENTRY, NULL, REMOVE_INVALID, SETVALUE_INVALID, size, threshold, values`

Constructor Summary
`protected` `AbstractLinkedMap()` Constructor only used in deserialization, do not use otherwise.
`protected` `AbstractLinkedMap(int initialCapacity)` Constructs a new, empty map with the specified initial capacity.
`protected` `AbstractLinkedMap(int initialCapacity, float loadFactor)` Constructs a new, empty map with the specified initial capacity and load factor.
`protected` `AbstractLinkedMap(int initialCapacity, float loadFactor, int threshold)` Constructor which performs no validation on the passed in parameters.
`protected` `AbstractLinkedMap(Map map)` Constructor copying elements from another map.

Method Summary
`protected void` `addEntry(AbstractHashedMap.HashEntry entry, int hashIndex)` Adds an entry into this map, maintaining insertion order.
`void` `clear()` Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.
`boolean` `containsValue(Object value)` Checks whether the map contains the specified value.
`protected AbstractHashedMap.HashEntry` `createEntry(AbstractHashedMap.HashEntry next, int hashCode, Object key, Object value)` Creates an entry to store the data.
`protected Iterator` `createEntrySetIterator()` Creates an entry set iterator.
`protected Iterator` `createKeySetIterator()` Creates a key set iterator.
`protected Iterator` `createValuesIterator()` Creates a values iterator.
`protected AbstractLinkedMap.LinkEntry` `entryAfter(AbstractLinkedMap.LinkEntry entry)` Gets the `after` field from a `LinkEntry`.
`protected AbstractLinkedMap.LinkEntry` `entryBefore(AbstractLinkedMap.LinkEntry entry)` Gets the `before` field from a `LinkEntry`.
`Object` `firstKey()` Gets the first key in the map, which is the most recently inserted.
`protected AbstractLinkedMap.LinkEntry` `getEntry(int index)` Gets the key at the specified index.
`protected void` `init()` Initialise this subclass during construction.
`Object` `lastKey()` Gets the last key in the map, which is the first inserted.
`MapIterator` `mapIterator()` Gets an iterator over the map.
`Object` `nextKey(Object key)` Gets the next key in sequence.
`OrderedMapIterator` `orderedMapIterator()` Gets a bidirectional iterator over the map.
`Object` `previousKey(Object key)` Gets the previous key in sequence.
`protected void` `removeEntry(AbstractHashedMap.HashEntry entry, int hashIndex, AbstractHashedMap.HashEntry previous)` Removes an entry from the map and the linked list.

Methods inherited from class org.apache.commons.collections.map.AbstractHashedMap
`addMapping, calculateNewCapacity, calculateThreshold, checkCapacity, clone, containsKey, convertKey, destroyEntry, doReadObject, doWriteObject, ensureCapacity, entryHashCode, entryKey, entryNext, entrySet, entryValue, equals, get, getEntry, hash, hashCode, hashIndex, isEmpty, isEqualKey, isEqualValue, keySet, put, putAll, remove, removeMapping, reuseEntry, size, toString, updateEntry, values`

Methods inherited from class java.lang.Object
`finalize, getClass, notify, notifyAll, wait, wait, wait`

Methods inherited from interface java.util.Map
`containsKey, entrySet, equals, get, hashCode, isEmpty, keySet, put, putAll, remove, size, values`

Field Detail

### header

    protected transient AbstractLinkedMap.LinkEntry header

  Header in the linked list

Constructor Detail

### AbstractLinkedMap

    protected AbstractLinkedMap()

  Constructor only used in deserialization, do not use otherwise.

### AbstractLinkedMap

    protected AbstractLinkedMap(int initialCapacity,
                                float loadFactor,
                                int threshold)

  Constructor which performs no validation on the passed in parameters.

Parameters:
  `initialCapacity` - the initial capacity, must be a power of two
  `loadFactor` - the load factor, must be > 0.0f and generally < 1.0f
  `threshold` - the threshold, must be sensible

### AbstractLinkedMap

    protected AbstractLinkedMap(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

### AbstractLinkedMap

    protected AbstractLinkedMap(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

### AbstractLinkedMap

    protected AbstractLinkedMap(Map map)

  Constructor copying elements from another map.

Parameters:
  `map` - the map to copy
Throws:
  `NullPointerException` - if the map is null

Method Detail

### init

    protected void init()

  Initialise this subclass during construction.

  Overrides:
    `init` in class `AbstractHashedMap`

### containsValue

    public boolean containsValue(Object value)

  Checks whether the map contains the specified value.

  Specified by:
    `containsValue` in interface `Map`
  Overrides:
    `containsValue` in class `AbstractHashedMap`
  Parameters:
    `value` - the value to search for
  Returns:
    true if the map contains the value

### clear

    public void clear()

  Clears the map, resetting the size to zero and nullifying references to avoid garbage collection issues.

  Specified by:
    `clear` in interface `Map`
  Overrides:
    `clear` in class `AbstractHashedMap`

### firstKey

    public Object firstKey()

  Gets the first key in the map, which is the most recently inserted.

  Specified by:
    `firstKey` in interface `OrderedMap`
  Returns:
    the most recently inserted key

### lastKey

    public Object lastKey()

  Gets the last key in the map, which is the first inserted.

  Specified by:
    `lastKey` in interface `OrderedMap`
  Returns:
    the eldest key

### nextKey

    public Object nextKey(Object key)

  Gets the next key in sequence.

  Specified by:
    `nextKey` in interface `OrderedMap`
  Parameters:
    `key` - the key to get after
  Returns:
    the next key

### previousKey

    public Object previousKey(Object key)

  Gets the previous key in sequence.

  Specified by:
    `previousKey` in interface `OrderedMap`
  Parameters:
    `key` - the key to get before
  Returns:
    the previous key

### getEntry

    protected AbstractLinkedMap.LinkEntry getEntry(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

### addEntry

    protected void addEntry(AbstractHashedMap.HashEntry entry,
                            int hashIndex)

  Adds an entry into this map, maintaining insertion order.

  This implementation adds the entry to the data storage table and to the end of the linked list.

  Overrides:
    `addEntry` in class `AbstractHashedMap`
  Parameters:
    `entry` - the entry to add
    `hashIndex` - the index into the data array to store at

### createEntry

    protected AbstractHashedMap.HashEntry createEntry(AbstractHashedMap.HashEntry next,
                                                      int hashCode,
                                                      Object key,
                                                      Object value)

  Creates an entry to store the data.

  This implementation creates a new LinkEntry instance.

  Overrides:
    `createEntry` in class `AbstractHashedMap`
  Parameters:
    `next` - the next entry in sequence
    `hashCode` - the hash code to use
    `key` - the key to store
    `value` - the value to store
  Returns:
    the newly created entry

### removeEntry

    protected void removeEntry(AbstractHashedMap.HashEntry entry,
                               int hashIndex,
                               AbstractHashedMap.HashEntry previous)

  Removes an entry from the map and the linked list.

  This implementation removes the entry from the linked list chain, then calls the superclass implementation.

  Overrides:
    `removeEntry` in class `AbstractHashedMap`
  Parameters:
    `entry` - the entry to remove
    `hashIndex` - the index into the data structure
    `previous` - the previous entry in the chain

### entryBefore

    protected AbstractLinkedMap.LinkEntry entryBefore(AbstractLinkedMap.LinkEntry entry)

  Gets the `before` field from a `LinkEntry`. Used in subclasses that have no visibility of the field.

  Parameters:
    `entry` - the entry to query, must not be null
  Returns:
    the `before` field of the entry
  Throws:
    `NullPointerException` - if the entry is null
  Since:
    Commons Collections 3.1

### entryAfter

    protected AbstractLinkedMap.LinkEntry entryAfter(AbstractLinkedMap.LinkEntry entry)

  Gets the `after` field from a `LinkEntry`. Used in subclasses that have no visibility of the field.

  Parameters:
    `entry` - the entry to query, must not be null
  Returns:
    the `after` field of the entry
  Throws:
    `NullPointerException` - if the entry is null
  Since:
    Commons Collections 3.1

### mapIterator

    public MapIterator mapIterator()

  Gets an iterator over the map. Changes made to the iterator affect this map.

  A MapIterator returns the keys in the map. It also provides convenient methods to get the key and value, and set the value. It avoids the need to create an entrySet/keySet/values object.

  Specified by:
    `mapIterator` in interface `IterableMap`
  Overrides:
    `mapIterator` in class `AbstractHashedMap`
  Returns:
    the map iterator

### orderedMapIterator

    public OrderedMapIterator orderedMapIterator()

  Gets a bidirectional iterator over the map. Changes made to the iterator affect this map.

  A MapIterator returns the keys in the map. It also provides convenient methods to get the key and value, and set the value. It avoids the need to create an entrySet/keySet/values object.

  Specified by:
    `orderedMapIterator` in interface `OrderedMap`
  Returns:
    the map iterator

### createEntrySetIterator

    protected Iterator createEntrySetIterator()

  Creates an entry set iterator. Subclasses can override this to return iterators with different properties.

  Overrides:
    `createEntrySetIterator` in class `AbstractHashedMap`
  Returns:
    the entrySet iterator

### createKeySetIterator

    protected Iterator createKeySetIterator()

  Creates a key set iterator. Subclasses can override this to return iterators with different properties.

  Overrides:
    `createKeySetIterator` in class `AbstractHashedMap`
  Returns:
    the keySet iterator

### createValuesIterator

    protected Iterator createValuesIterator()

  Creates a values iterator. Subclasses can override this to return iterators with different properties.

  Overrides:
    `createValuesIterator` in class `AbstractHashedMap`
  Returns:
    the values iterator

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