Package org.apache.commons.collections4.map

Class AbstractHashedMap<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:
    Map<K,​V>, Get<K,​V>, IterableGet<K,​V>, IterableMap<K,​V>, Put<K,​V>
    Direct Known Subclasses:
    AbstractLinkedMap, AbstractReferenceMap, CaseInsensitiveMap, HashedMap
    public class AbstractHashedMap<K,​V>
extends AbstractMap<K,​V>
implements IterableMap<K,​V>
    An abstract implementation of a hash-based map which provides numerous points for subclasses to override.

    This class implements all the features necessary for a subclass hash-based map. Key-value entries are stored in instances of the HashEntry 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.

    NOTE: From Commons Collections 3.1 this class extends AbstractMap. This is to provide backwards compatibility for ReferenceMap between v3.0 and v3.1. This extends clause will be removed in v5.0.

    Since:
    3.0

    • Method Detail

      • get

        public V get​(Object key)
        Gets the value mapped to the key specified.
        Specified by:
        get in interface Get<K,​V>
        Specified by:
        get in interface Map<K,​V>
        Overrides:
        get in class AbstractMap<K,​V>
        Parameters:
        key - the key
        Returns:
        the mapped value, null if no match
        See Also:
        Map.get(Object)

      • size

        public int size()
        Gets the size of the map.
        Specified by:
        size in interface Get<K,​V>
        Specified by:
        size in interface Map<K,​V>
        Overrides:
        size in class AbstractMap<K,​V>
        Returns:
        the size
        See Also:
        Map.size()

      • isEmpty

        public boolean isEmpty()
        Checks whether the map is currently empty.
        Specified by:
        isEmpty in interface Get<K,​V>
        Specified by:
        isEmpty in interface Map<K,​V>
        Overrides:
        isEmpty in class AbstractMap<K,​V>
        Returns:
        true if the map is currently size zero
        See Also:
        Map.isEmpty()

      • put

        public V put​(K key,
             V value)
        Puts a key-value mapping into this map.
        Specified by:
        put in interface Map<K,​V>
        Specified by:
        put in interface Put<K,​V>
        Overrides:
        put in class AbstractMap<K,​V>
        Parameters:
        key - the key to add
        value - the value to add
        Returns:
        the value previously mapped to this key, null if none
        See Also:
        Map.put(Object, Object)

      • remove

        public V remove​(Object key)
        Removes the specified mapping from this map.
        Specified by:
        remove in interface Get<K,​V>
        Specified by:
        remove in interface Map<K,​V>
        Overrides:
        remove in class AbstractMap<K,​V>
        Parameters:
        key - the mapping to remove
        Returns:
        the value mapped to the removed key, null if key not in map
        See Also:
        Map.remove(Object)

      • 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<K,​V>
        Specified by:
        clear in interface Put<K,​V>
        Overrides:
        clear in class AbstractMap<K,​V>
        See Also:
        Map.clear()

      • mapIterator

        public MapIterator<K,​V> 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. It also avoids creating the Map.Entry object.

        Specified by:
        mapIterator in interface IterableGet<K,​V>
        Returns:
        the map iterator

      • keySet

        public Set<K> keySet()
        Gets the keySet view of the map. Changes made to the view affect this map. To simply iterate through the keys, use mapIterator().
        Specified by:
        keySet in interface Get<K,​V>
        Specified by:
        keySet in interface Map<K,​V>
        Overrides:
        keySet in class AbstractMap<K,​V>
        Returns:
        the keySet view
        See Also:
        Map.keySet()

      • equals

        public boolean equals​(Object obj)
        Compares this map with another.
        Specified by:
        equals in interface Map<K,​V>
        Overrides:
        equals in class AbstractMap<K,​V>
        Parameters:
        obj - the object to compare to
        Returns:
        true if equal

      • hashCode

        public int hashCode()
        Gets the standard Map hashCode.
        Specified by:
        hashCode in interface Map<K,​V>
        Overrides:
        hashCode in class AbstractMap<K,​V>
        Returns:
        the hash code defined in the Map interface

      • toString

        public String toString()
        Gets the map as a String.
        Overrides:
        toString in class AbstractMap<K,​V>
        Returns:
        a string version of the map