Package org.apache.commons.collections4.map

Class AbstractHashedMap<K,V>

java.lang.Object
java.util.AbstractMap<K,V>
org.apache.commons.collections4.map.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 behavior, 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

  • Field Details

  • Constructor Details

    • AbstractHashedMap

      protected AbstractHashedMap()
      Constructor only used in deserialization, do not use otherwise.

    • AbstractHashedMap

      protected AbstractHashedMap(int initialCapacity)
      Constructs a new, empty map with the specified initial capacity and default load factor.
      Parameters:
      initialCapacity - the initial capacity
      Throws:
      IllegalArgumentException - if the initial capacity is negative

    • AbstractHashedMap

      protected AbstractHashedMap(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 or equal to zero

    • AbstractHashedMap

      protected AbstractHashedMap(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

    • AbstractHashedMap

      protected AbstractHashedMap(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

    • addEntry

      protected void addEntry(AbstractHashedMap.HashEntry<K,V> entry, int hashIndex)
      Adds an entry into this map.

      This implementation adds the entry to the data storage table. Subclasses could override to handle changes to the map.

      Parameters:
      entry - the entry to add
      hashIndex - the index into the data array to store at

    • addMapping

      protected void addMapping(int hashIndex, int hashCode, K key, V value)
      Adds a new key-value mapping into this map.

      This implementation calls createEntry(), addEntry() and checkCapacity(). It also handles changes to modCount and size. Subclasses could override to fully control adds to the map.

      Parameters:
      hashIndex - the index into the data array to store at
      hashCode - the hash code of the key to add
      key - the key to add
      value - the value to add

    • calculateNewCapacity

      protected int calculateNewCapacity(int proposedCapacity)
      Calculates the new capacity of the map. This implementation normalizes the capacity to a power of two.
      Parameters:
      proposedCapacity - the proposed capacity
      Returns:
      the normalized new capacity

    • calculateThreshold

      protected int calculateThreshold(int newCapacity, float factor)
      Calculates the new threshold of the map, where it will be resized. This implementation uses the load factor.
      Parameters:
      newCapacity - the new capacity
      factor - the load factor
      Returns:
      the new resize threshold

    • checkCapacity

      protected void checkCapacity()
      Checks the capacity of the map and enlarges it if necessary.

      This implementation uses the threshold to check if the map needs enlarging

    • 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:

    • clone

      protected AbstractHashedMap<K,V> clone()
      Clones the map without cloning the keys or values.

      To implement clone(), a subclass must implement the Cloneable interface and make this method public.

      Overrides:
      clone in class AbstractMap<K,V>
      Returns:
      a shallow clone
      Throws:
      InternalError - if AbstractMap.clone() failed

    • containsKey

      public boolean containsKey(Object key)
      Checks whether the map contains the specified key.
      Specified by:
      containsKey in interface Get<K,V>
      Specified by:
      containsKey in interface Map<K,V>
      Overrides:
      containsKey in class AbstractMap<K,V>
      Parameters:
      key - the key to search for
      Returns:
      true if the map contains the key
      See Also:

    • containsValue

      public boolean containsValue(Object value)
      Checks whether the map contains the specified value.
      Specified by:
      containsValue in interface Get<K,V>
      Specified by:
      containsValue in interface Map<K,V>
      Overrides:
      containsValue in class AbstractMap<K,V>
      Parameters:
      value - the value to search for
      Returns:
      true if the map contains the value
      See Also:

    • convertKey

      protected Object convertKey(Object key)
      Converts input keys to another object for storage in the map. This implementation masks nulls. Subclasses can override this to perform alternate key conversions.

      The reverse conversion can be changed, if required, by overriding the getKey() method in the hash entry.

      Parameters:
      key - the key convert
      Returns:
      the converted key

    • createEntry

      protected AbstractHashedMap.HashEntry<K,V> createEntry(AbstractHashedMap.HashEntry<K,V> next, int hashCode, K key, V value)
      Creates an entry to store the key-value data.

      This implementation creates a new HashEntry instance. Subclasses can override this to return a different storage class, or implement caching.

      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

    • createEntrySetIterator

      protected Iterator<Map.Entry<K,V>> createEntrySetIterator()
      Creates an entry set iterator. Subclasses can override this to return iterators with different properties.
      Returns:
      the entrySet iterator

    • createKeySetIterator

      protected Iterator<K> createKeySetIterator()
      Creates a key set iterator. Subclasses can override this to return iterators with different properties.
      Returns:
      the keySet iterator

    • createValuesIterator

      protected Iterator<V> createValuesIterator()
      Creates a values iterator. Subclasses can override this to return iterators with different properties.
      Returns:
      the values iterator

    • destroyEntry

      protected void destroyEntry(AbstractHashedMap.HashEntry<K,V> entry)
      Kills an entry ready for the garbage collector.

      This implementation prepares the HashEntry for garbage collection. Subclasses can override this to implement caching (override clear as well).

      Parameters:
      entry - the entry to destroy

    • doReadObject

      protected void doReadObject(ObjectInputStream in) throws IOException, ClassNotFoundException
      Reads the map data from the stream. This method must be overridden if a subclass must be setup before put() is used.

      Serialization is not one of the JDK's nicest topics. Normal serialization will initialize the superclass before the subclass. Sometimes however, this isn't what you want, as in this case the put() method on read can be affected by subclass state.

      The solution adopted here is to deserialize the state data of this class in this protected method. This method must be called by the readObject() of the first serializable subclass.

      Subclasses may override if the subclass has a specific field that must be present before put() or calculateThreshold() will work correctly.

      Parameters:
      in - the input stream
      Throws:
      IOException - if an error occurs while reading from the stream
      ClassNotFoundException - if an object read from the stream can not be loaded

    • doWriteObject

      protected void doWriteObject(ObjectOutputStream out) throws IOException
      Writes the map data to the stream. This method must be overridden if a subclass must be setup before put() is used.

      Serialization is not one of the JDK's nicest topics. Normal serialization will initialize the superclass before the subclass. Sometimes however, this isn't what you want, as in this case the put() method on read can be affected by subclass state.

      The solution adopted here is to serialize the state data of this class in this protected method. This method must be called by the writeObject() of the first serializable subclass.

      Subclasses may override if they have a specific field that must be present on read before this implementation will work. Generally, the read determines what must be serialized here, if anything.

      Parameters:
      out - the output stream
      Throws:
      IOException - if an error occurs while writing to the stream

    • ensureCapacity

      protected void ensureCapacity(int newCapacity)
      Changes the size of the data structure to the capacity proposed.
      Parameters:
      newCapacity - the new capacity of the array (a power of two, less or equal to max)

    • entryHashCode

      protected int entryHashCode(AbstractHashedMap.HashEntry<K,V> entry)
      Gets the hashCode field from a HashEntry. Used in subclasses that have no visibility of the field.
      Parameters:
      entry - the entry to query, must not be null
      Returns:
      the hashCode field of the entry
      Throws:
      NullPointerException - if the entry is null
      Since:
      3.1

    • entryKey

      protected K entryKey(AbstractHashedMap.HashEntry<K,V> entry)
      Gets the key field from a HashEntry. Used in subclasses that have no visibility of the field.
      Parameters:
      entry - the entry to query, must not be null
      Returns:
      the key field of the entry
      Throws:
      NullPointerException - if the entry is null
      Since:
      3.1

    • entryNext

      protected AbstractHashedMap.HashEntry<K,V> entryNext(AbstractHashedMap.HashEntry<K,V> entry)
      Gets the next field from a HashEntry. Used in subclasses that have no visibility of the field.
      Parameters:
      entry - the entry to query, must not be null
      Returns:
      the next field of the entry
      Throws:
      NullPointerException - if the entry is null
      Since:
      3.1

    • entrySet

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

    • entryValue

      protected V entryValue(AbstractHashedMap.HashEntry<K,V> entry)
      Gets the value field from a HashEntry. Used in subclasses that have no visibility of the field.
      Parameters:
      entry - the entry to query, must not be null
      Returns:
      the value field of the entry
      Throws:
      NullPointerException - if the entry is null
      Since:
      3.1

    • 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

    • 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:

    • getEntry

      protected AbstractHashedMap.HashEntry<K,V> getEntry(Object key)
      Gets the entry mapped to the key specified.

      This method exists for subclasses that may need to perform a multi-step process accessing the entry. The public methods in this class don't use this method to gain a small performance boost.

      Parameters:
      key - the key
      Returns:
      the entry, null if no match

    • hash

      protected int hash(Object key)
      Gets the hash code for the key specified. This implementation uses the additional hashing routine from JDK1.4. Subclasses can override this to return alternate hash codes.
      Parameters:
      key - the key to get a hash code for
      Returns:
      the hash code

    • 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

    • hashIndex

      protected int hashIndex(int hashCode, int dataSize)
      Gets the index into the data storage for the hashCode specified. This implementation uses the least significant bits of the hashCode. Subclasses can override this to return alternate bucketing.
      Parameters:
      hashCode - the hash code to use
      dataSize - the size of the data to pick a bucket from
      Returns:
      the bucket index

    • init

      protected void init()
      Initialize subclasses during construction, cloning or deserialization.

    • 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:

    • isEqualKey

      protected boolean isEqualKey(Object key1, Object key2)
      Compares two keys, in internal converted form, to see if they are equal. This implementation uses the equals method and assumes neither key is null. Subclasses can override this to match differently.
      Parameters:
      key1 - the first key to compare passed in from outside
      key2 - the second key extracted from the entry via entry.key
      Returns:
      true if equal

    • isEqualValue

      protected boolean isEqualValue(Object value1, Object value2)
      Compares two values, in external form, to see if they are equal. This implementation uses the equals method and assumes neither value is null. Subclasses can override this to match differently.
      Parameters:
      value1 - the first value to compare passed in from outside
      value2 - the second value extracted from the entry via getValue()
      Returns:
      true if equal

    • 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:

    • 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

    • 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:

    • putAll

      public void putAll(Map<? extends K,? extends V> map)
      Puts all the values from the specified map into this map.

      This implementation iterates around the specified map and uses put(Object, Object).

      Specified by:
      putAll in interface Map<K,V>
      Specified by:
      putAll in interface Put<K,V>
      Overrides:
      putAll in class AbstractMap<K,V>
      Parameters:
      map - the map to add
      Throws:
      NullPointerException - if the map is null
      See Also:

    • 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:

    • removeEntry

      protected void removeEntry(AbstractHashedMap.HashEntry<K,V> entry, int hashIndex, AbstractHashedMap.HashEntry<K,V> previous)
      Removes an entry from the chain stored in a particular index.

      This implementation removes the entry from the data storage table. The size is not updated. Subclasses could override to handle changes to the map.

      Parameters:
      entry - the entry to remove
      hashIndex - the index into the data structure
      previous - the previous entry in the chain

    • removeMapping

      protected void removeMapping(AbstractHashedMap.HashEntry<K,V> entry, int hashIndex, AbstractHashedMap.HashEntry<K,V> previous)
      Removes a mapping from the map.

      This implementation calls removeEntry() and destroyEntry(). It also handles changes to modCount and size. Subclasses could override to fully control removals from the map.

      Parameters:
      entry - the entry to remove
      hashIndex - the index into the data structure
      previous - the previous entry in the chain

    • reuseEntry

      protected void reuseEntry(AbstractHashedMap.HashEntry<K,V> entry, int hashIndex, int hashCode, K key, V value)
      Reuses an existing key-value mapping, storing completely new data.

      This implementation sets all the data fields on the entry. Subclasses could populate additional entry fields.

      Parameters:
      entry - the entry to update, not null
      hashIndex - the index in the data array
      hashCode - the hash code of the key to add
      key - the key to add
      value - the value to add

    • 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:

    • toString

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

    • updateEntry

      protected void updateEntry(AbstractHashedMap.HashEntry<K,V> entry, V newValue)
      Updates an existing key-value mapping to change the value.

      This implementation calls setValue() on the entry. Subclasses could override to handle changes to the map.

      Parameters:
      entry - the entry to update
      newValue - the new value to store

    • values

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