Package it.unimi.dsi.fastutil.objects

Class Object2ObjectLinkedOpenCustomHashMap<K,​V>

  • All Implemented Interfaces:
    Function<K,​V>, Hash, Object2ObjectFunction<K,​V>, Object2ObjectMap<K,​V>, Object2ObjectSortedMap<K,​V>, Serializable, Cloneable, Function<K,​V>, Map<K,​V>, SortedMap<K,​V>
    public class Object2ObjectLinkedOpenCustomHashMap<K,​V>
extends AbstractObject2ObjectSortedMap<K,​V>
implements Serializable, Cloneable, Hash
    A type-specific linked hash map with with a fast, small-footprint implementation.

    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.

    Iterators generated by this map will enumerate pairs in the same order in which they have been added to the map (addition of pairs whose key is already present in the map does not change the iteration order). Note that this order has nothing in common with the natural order of the keys. The order is kept by means of a doubly linked list, represented via an array of longs parallel to the table.

    This class implements the interface of a sorted map, so to allow easy access of the iteration order: for instance, you can get the first key in iteration order with firstKey() without having to create an iterator; however, this class partially violates the SortedMap contract because all submap methods throw an exception and comparator() returns always null.

    Additional methods, such as getAndMoveToFirst(), make it easy to use instances of this class as a cache (e.g., with LRU policy).

    The iterators provided by the views of this class using are type-specific list iterators, and can be started at any element which is a key of the map, or a NoSuchElementException exception will be thrown. If, however, the provided element is not the first or last key in the map, the first access to the list index will require linear time, as in the worst case the entire key set must be scanned in iteration order to retrieve the positional index of the starting key. If you use just the methods of a type-specific BidirectionalIterator, however, all operations will be performed in constant time.

    See Also:
    Hash, HashCommon, Serialized Form

    • Constructor Detail

      • Object2ObjectLinkedOpenCustomHashMap

        public Object2ObjectLinkedOpenCustomHashMap​(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.

      • Object2ObjectLinkedOpenCustomHashMap

        public Object2ObjectLinkedOpenCustomHashMap​(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.

      • Object2ObjectLinkedOpenCustomHashMap

        public Object2ObjectLinkedOpenCustomHashMap​(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.

      • Object2ObjectLinkedOpenCustomHashMap

        public Object2ObjectLinkedOpenCustomHashMap​(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.

      • Object2ObjectLinkedOpenCustomHashMap

        public Object2ObjectLinkedOpenCustomHashMap​(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.

      • Object2ObjectLinkedOpenCustomHashMap

        public Object2ObjectLinkedOpenCustomHashMap​(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.

      • Object2ObjectLinkedOpenCustomHashMap

        public Object2ObjectLinkedOpenCustomHashMap​(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.

      • Object2ObjectLinkedOpenCustomHashMap

        public Object2ObjectLinkedOpenCustomHashMap​(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.

      • removeFirst

        public V removeFirst()
        Removes the mapping associated with the first key in iteration order.
        Returns:
        the value previously associated with the first key in iteration order.
        Throws:
        NoSuchElementException - is this map is empty.

      • removeLast

        public V removeLast()
        Removes the mapping associated with the last key in iteration order.
        Returns:
        the value previously associated with the last key in iteration order.
        Throws:
        NoSuchElementException - is this map is empty.

      • getAndMoveToFirst

        public V getAndMoveToFirst​(K k)
        Returns the value to which the given key is mapped; if the key is present, it is moved to the first position of the iteration order.
        Parameters:
        k - the key.
        Returns:
        the corresponding value, or the default return value if no value was present for the given key.

      • getAndMoveToLast

        public V getAndMoveToLast​(K k)
        Returns the value to which the given key is mapped; if the key is present, it is moved to the last position of the iteration order.
        Parameters:
        k - the key.
        Returns:
        the corresponding value, or the default return value if no value was present for the given key.

      • putAndMoveToFirst

        public V putAndMoveToFirst​(K k,
                           V v)
        Adds a pair to the map; if the key is already present, it is moved to the first position of the iteration order.
        Parameters:
        k - the key.
        v - the value.
        Returns:
        the old value, or the default return value if no value was present for the given key.

      • putAndMoveToLast

        public V putAndMoveToLast​(K k,
                          V v)
        Adds a pair to the map; if the key is already present, it is moved to the last position of the iteration order.
        Parameters:
        k - the key.
        v - the value.
        Returns:
        the old value, or the default return value if no value was present for the given key.

      • firstKey

        public K firstKey()
        Returns the first key of this map in iteration order.
        Specified by:
        firstKey in interface SortedMap<K,​V>
        Returns:
        the first key in iteration order.

      • lastKey

        public K lastKey()
        Returns the last key of this map in iteration order.
        Specified by:
        lastKey in interface SortedMap<K,​V>
        Returns:
        the last key in iteration order.

      • keySet

        public ObjectSortedSet<K> keySet()
        Description copied from class: AbstractObject2ObjectSortedMap
        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.

        The view is backed by the sorted 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>
        Specified by:
        keySet in interface Object2ObjectSortedMap<K,​V>
        Specified by:
        keySet in interface SortedMap<K,​V>
        Overrides:
        keySet in class AbstractObject2ObjectSortedMap<K,​V>
        Returns:
        a sorted 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: AbstractObject2ObjectSortedMap
        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.

        The view is backed by the sorted 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>
        Specified by:
        values in interface Object2ObjectSortedMap<K,​V>
        Specified by:
        values in interface SortedMap<K,​V>
        Overrides:
        values in class AbstractObject2ObjectSortedMap<K,​V>
        Returns:
        a type-specific collection view of the values contained in this map.
        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 Object2ObjectLinkedOpenCustomHashMap<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.