Package org.apache.commons.collections.map

Class AbstractLinkedMap

  • All Implemented Interfaces:
    Map, IterableMap, 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: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
    Author:
    java util LinkedHashMap, Stephen Colebourne

    • 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

      • 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

      • 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

      • 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