Package org.apache.commons.collections.map

Class AbstractHashedMap

  • All Implemented Interfaces:
    Map, IterableMap
    Direct Known Subclasses:
    AbstractLinkedMap, AbstractReferenceMap, CaseInsensitiveMap, HashedMap, IdentityMap
    public class AbstractHashedMap
extends AbstractMap
implements IterableMap
    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 v4.0.

    Since:
    Commons Collections 3.0
    Version:
    $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
    Author:
    java util HashMap, Stephen Colebourne, Christian Siefkes

    • Constructor Detail

      • AbstractHashedMap

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

      • 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​(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 less than one

      • 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 less than one
        IllegalArgumentException - if the load factor is less than or equal to zero

      • AbstractHashedMap

        protected AbstractHashedMap​(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 subclasses during construction, cloning or deserialization.

      • get

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

      • size

        public int size()
        Gets the size of the map.
        Specified by:
        size in interface Map
        Overrides:
        size in class AbstractMap
        Returns:
        the size

      • isEmpty

        public boolean isEmpty()
        Checks whether the map is currently empty.
        Specified by:
        isEmpty in interface Map
        Overrides:
        isEmpty in class AbstractMap
        Returns:
        true if the map is currently size zero

      • containsKey

        public boolean containsKey​(Object key)
        Checks whether the map contains the specified key.
        Specified by:
        containsKey in interface Map
        Overrides:
        containsKey in class AbstractMap
        Parameters:
        key - the key to search for
        Returns:
        true if the map contains the key

      • containsValue

        public boolean containsValue​(Object value)
        Checks whether the map contains the specified value.
        Specified by:
        containsValue in interface Map
        Overrides:
        containsValue in class AbstractMap
        Parameters:
        value - the value to search for
        Returns:
        true if the map contains the value

      • put

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

      • putAll

        public void putAll​(Map 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
        Overrides:
        putAll in class AbstractMap
        Parameters:
        map - the map to add
        Throws:
        NullPointerException - if the map is null

      • remove

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

      • 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 AbstractMap

      • 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

      • 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

      • 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

      • 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

      • getEntry

        protected AbstractHashedMap.HashEntry 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

      • updateEntry

        protected void updateEntry​(AbstractHashedMap.HashEntry entry,
                           Object 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

      • reuseEntry

        protected void reuseEntry​(AbstractHashedMap.HashEntry entry,
                          int hashIndex,
                          int hashCode,
                          Object key,
                          Object 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

      • addMapping

        protected void addMapping​(int hashIndex,
                          int hashCode,
                          Object key,
                          Object 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

      • createEntry

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

      • addEntry

        protected void addEntry​(AbstractHashedMap.HashEntry 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

      • removeMapping

        protected void removeMapping​(AbstractHashedMap.HashEntry entry,
                             int hashIndex,
                             AbstractHashedMap.HashEntry 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

      • removeEntry

        protected void removeEntry​(AbstractHashedMap.HashEntry entry,
                           int hashIndex,
                           AbstractHashedMap.HashEntry 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

      • destroyEntry

        protected void destroyEntry​(AbstractHashedMap.HashEntry 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

      • 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

      • 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)

      • 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

      • entryNext

        protected AbstractHashedMap.HashEntry entryNext​(AbstractHashedMap.HashEntry 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:
        Commons Collections 3.1

      • entryHashCode

        protected int entryHashCode​(AbstractHashedMap.HashEntry 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:
        Commons Collections 3.1

      • entryKey

        protected Object entryKey​(AbstractHashedMap.HashEntry 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:
        Commons Collections 3.1

      • entryValue

        protected Object entryValue​(AbstractHashedMap.HashEntry 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:
        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. It also avoids creating the Map.Entry object.

        Specified by:
        mapIterator in interface IterableMap
        Returns:
        the map iterator

      • entrySet

        public Set 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 Map
        Specified by:
        entrySet in class AbstractMap
        Returns:
        the entrySet view

      • createEntrySetIterator

        protected Iterator createEntrySetIterator()
        Creates an entry set iterator. Subclasses can override this to return iterators with different properties.
        Returns:
        the entrySet iterator

      • keySet

        public Set 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 Map
        Overrides:
        keySet in class AbstractMap
        Returns:
        the keySet view

      • createKeySetIterator

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

      • values

        public Collection 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 Map
        Overrides:
        values in class AbstractMap
        Returns:
        the values view

      • createValuesIterator

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

      • 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 initialise 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

      • 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 initialise 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
        ClassNotFoundException

      • clone

        protected Object 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
        Returns:
        a shallow clone

      • equals

        public boolean equals​(Object obj)
        Compares this map with another.
        Specified by:
        equals in interface Map
        Overrides:
        equals in class AbstractMap
        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
        Overrides:
        hashCode in class AbstractMap
        Returns:
        the hash code defined in the Map interface

      • toString

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