Class Object2ObjectOpenCustomHashMap<K,​V>

  • All Implemented Interfaces:
    Function<K,​V>, Hash, Object2ObjectFunction<K,​V>, Object2ObjectMap<K,​V>, Serializable, Cloneable, Function<K,​V>, Map<K,​V>

    public class Object2ObjectOpenCustomHashMap<K,​V>
    extends AbstractObject2ObjectMap<K,​V>
    implements Serializable, Cloneable, Hash
    A type-specific hash map with a fast, small-footprint implementation whose hashing strategy is specified at creation time.

    Instances of this class use a hash table to represent a map. The table is filled up to a specified load factor, and then doubled in size to accommodate new entries. If the table is emptied below one fourth of the load factor, it is halved in size; however, the table is never reduced to a size smaller than that at creation time: this approach makes it possible to create maps with a large capacity in which insertions and deletions do not cause immediately rehashing. Moreover, halving is not performed when deleting entries from an iterator, as it would interfere with the iteration process.

    Note that clear() does not modify the hash table size. Rather, a family of trimming methods lets you control the size of the table; this is particularly useful if you reuse instances of this class.

    See Also:
    Hash, HashCommon, Serialized Form
    • Constructor Detail

      • Object2ObjectOpenCustomHashMap

        public Object2ObjectOpenCustomHashMap​(int expected,
                                              float f,
                                              Hash.Strategy<? super K> strategy)
        Creates a new hash map.

        The actual table size will be the least power of two greater than expected/f.

        Parameters:
        expected - the expected number of elements in the hash map.
        f - the load factor.
        strategy - the strategy.
      • Object2ObjectOpenCustomHashMap

        public Object2ObjectOpenCustomHashMap​(int expected,
                                              Hash.Strategy<? super K> strategy)
        Creates a new hash map with Hash.DEFAULT_LOAD_FACTOR as load factor.
        Parameters:
        expected - the expected number of elements in the hash map.
        strategy - the strategy.
      • Object2ObjectOpenCustomHashMap

        public Object2ObjectOpenCustomHashMap​(Map<? extends K,​? extends V> m,
                                              float f,
                                              Hash.Strategy<? super K> strategy)
        Creates a new hash map copying a given one.
        Parameters:
        m - a Map to be copied into the new hash map.
        f - the load factor.
        strategy - the strategy.
      • Object2ObjectOpenCustomHashMap

        public Object2ObjectOpenCustomHashMap​(Map<? extends K,​? extends V> m,
                                              Hash.Strategy<? super K> strategy)
        Creates a new hash map with Hash.DEFAULT_LOAD_FACTOR as load factor copying a given one.
        Parameters:
        m - a Map to be copied into the new hash map.
        strategy - the strategy.
      • Object2ObjectOpenCustomHashMap

        public Object2ObjectOpenCustomHashMap​(Object2ObjectMap<K,​V> m,
                                              float f,
                                              Hash.Strategy<? super K> strategy)
        Creates a new hash map copying a given type-specific one.
        Parameters:
        m - a type-specific map to be copied into the new hash map.
        f - the load factor.
        strategy - the strategy.
      • Object2ObjectOpenCustomHashMap

        public Object2ObjectOpenCustomHashMap​(Object2ObjectMap<K,​V> m,
                                              Hash.Strategy<? super K> strategy)
        Creates a new hash map with Hash.DEFAULT_LOAD_FACTOR as load factor copying a given type-specific one.
        Parameters:
        m - a type-specific map to be copied into the new hash map.
        strategy - the strategy.
      • Object2ObjectOpenCustomHashMap

        public Object2ObjectOpenCustomHashMap​(K[] k,
                                              V[] v,
                                              float f,
                                              Hash.Strategy<? super K> strategy)
        Creates a new hash map using the elements of two parallel arrays.
        Parameters:
        k - the array of keys of the new hash map.
        v - the array of corresponding values in the new hash map.
        f - the load factor.
        strategy - the strategy.
        Throws:
        IllegalArgumentException - if k and v have different lengths.
      • Object2ObjectOpenCustomHashMap

        public Object2ObjectOpenCustomHashMap​(K[] k,
                                              V[] v,
                                              Hash.Strategy<? super K> strategy)
        Creates a new hash map with Hash.DEFAULT_LOAD_FACTOR as load factor using the elements of two parallel arrays.
        Parameters:
        k - the array of keys of the new hash map.
        v - the array of corresponding values in the new hash map.
        strategy - the strategy.
        Throws:
        IllegalArgumentException - if k and v have different lengths.
    • Method Detail

      • strategy

        public Hash.Strategy<? super K> strategy()
        Returns the hashing strategy.
        Returns:
        the hashing strategy of this custom hash map.
      • object2ObjectEntrySet

        public Object2ObjectMap.FastEntrySet<K,​V> object2ObjectEntrySet()
        Description copied from interface: Object2ObjectMap
        Returns a type-specific set view of the mappings contained in this map.

        This method is necessary because there is no inheritance along type parameters: it is thus impossible to strengthen Map.entrySet() so that it returns an ObjectSet of type-specific entries (the latter makes it possible to access keys and values with type-specific methods).

        Specified by:
        object2ObjectEntrySet in interface Object2ObjectMap<K,​V>
        Returns:
        a type-specific set view of the mappings contained in this map.
        See Also:
        Map.entrySet()
      • keySet

        public ObjectSet<K> keySet()
        Description copied from class: AbstractObject2ObjectMap
        Returns a type-specific-set view of the keys of this map.

        The view is backed by the set returned by Map.entrySet(). Note that no attempt is made at caching the result of this method, as this would require adding some attributes that lightweight implementations would not need. Subclasses may easily override this policy by calling this method and caching the result, but implementors are encouraged to write more efficient ad-hoc implementations.

        Specified by:
        keySet in interface Map<K,​V>
        Specified by:
        keySet in interface Object2ObjectMap<K,​V>
        Overrides:
        keySet in class AbstractObject2ObjectMap<K,​V>
        Returns:
        a set view of the keys of this map; it may be safely cast to a type-specific interface.
        See Also:
        Map.keySet()
      • values

        public ObjectCollection<V> values()
        Description copied from class: AbstractObject2ObjectMap
        Returns a type-specific-set view of the values of this map.

        The view is backed by the set returned by Map.entrySet(). Note that no attempt is made at caching the result of this method, as this would require adding some attributes that lightweight implementations would not need. Subclasses may easily override this policy by calling this method and caching the result, but implementors are encouraged to write more efficient ad-hoc implementations.

        Specified by:
        values in interface Map<K,​V>
        Specified by:
        values in interface Object2ObjectMap<K,​V>
        Overrides:
        values in class AbstractObject2ObjectMap<K,​V>
        Returns:
        a set view of the values of this map; it may be safely cast to a type-specific interface.
        See Also:
        Map.values()
      • trim

        public boolean trim()
        Rehashes the map, making the table as small as possible.

        This method rehashes the table to the smallest size satisfying the load factor. It can be used when the set will not be changed anymore, so to optimize access speed and size.

        If the table size is already the minimum possible, this method does nothing.

        Returns:
        true if there was enough memory to trim the map.
        See Also:
        trim(int)
      • trim

        public boolean trim​(int n)
        Rehashes this map if the table is too large.

        Let N be the smallest table size that can hold max(n,size()) entries, still satisfying the load factor. If the current table size is smaller than or equal to N, this method does nothing. Otherwise, it rehashes this map in a table of size N.

        This method is useful when reusing maps. Clearing a map leaves the table size untouched. If you are reusing a map many times, you can call this method with a typical size to avoid keeping around a very large table just because of a few large transient maps.

        Parameters:
        n - the threshold for the trimming.
        Returns:
        true if there was enough memory to trim the map.
        See Also:
        trim()
      • clone

        public Object2ObjectOpenCustomHashMap<K,​V> clone()
        Returns a deep copy of this map.

        This method performs a deep copy of this hash map; the data stored in the map, however, is not cloned. Note that this makes a difference only for object keys.

        Returns:
        a deep copy of this map.
      • hashCode

        public int hashCode()
        Returns a hash code for this map. This method overrides the generic method provided by the superclass. Since equals() is not overriden, it is important that the value returned by this method is the same value as the one returned by the overriden method.
        Specified by:
        hashCode in interface Map<K,​V>
        Overrides:
        hashCode in class AbstractObject2ObjectMap<K,​V>
        Returns:
        a hash code for this map.