Package it.unimi.dsi.fastutil.objects

Class Object2ObjectOpenHashMap<K,​V>

java.lang.Object
it.unimi.dsi.fastutil.objects.AbstractObject2ObjectFunction<K,​V>
it.unimi.dsi.fastutil.objects.AbstractObject2ObjectMap<K,​V>
it.unimi.dsi.fastutil.objects.Object2ObjectOpenHashMap<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 Object2ObjectOpenHashMap<K,​V>
extends AbstractObject2ObjectMap<K,​V>
implements Serializable, Cloneable, Hash
A type-specific hash map 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.

See Also:
Hash, HashCommon, Serialized Form

  • Constructor Details

    • Object2ObjectOpenHashMap

      public Object2ObjectOpenHashMap​(int expected, float f)
      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.

    • Object2ObjectOpenHashMap

      public Object2ObjectOpenHashMap​(int expected)
      Creates a new hash map with Hash.DEFAULT_LOAD_FACTOR as load factor.
      Parameters:
      expected - the expected number of elements in the hash map.

    • Object2ObjectOpenHashMap

      public Object2ObjectOpenHashMap()
      Creates a new hash map with initial expected Hash.DEFAULT_INITIAL_SIZE entries and Hash.DEFAULT_LOAD_FACTOR as load factor.

    • Object2ObjectOpenHashMap

      public Object2ObjectOpenHashMap​(Map<? extends K,​? extends V> m, float f)
      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.

    • Object2ObjectOpenHashMap

      public Object2ObjectOpenHashMap​(Map<? extends K,​? extends V> m)
      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.

    • Object2ObjectOpenHashMap

      public Object2ObjectOpenHashMap​(Object2ObjectMap<K,​V> m, float f)
      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.

    • Object2ObjectOpenHashMap

      public Object2ObjectOpenHashMap​(Object2ObjectMap<K,​V> m)
      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.

    • Object2ObjectOpenHashMap

      public Object2ObjectOpenHashMap​(K[] k, V[] v, float f)
      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.
      Throws:
      IllegalArgumentException - if k and v have different lengths.

    • Object2ObjectOpenHashMap

      public Object2ObjectOpenHashMap​(K[] k, V[] v)
      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.
      Throws:
      IllegalArgumentException - if k and v have different lengths.

  • Method Details

    • putAll

      public void putAll​(Map<? extends K,​? extends V> m)
      Description copied from class: AbstractObject2ObjectMap
      Specified by:
      putAll in interface Map<K,​V>
      Overrides:
      putAll in class AbstractObject2ObjectMap<K,​V>

    • put

      public V put​(K k, V v)
      Description copied from interface: Object2ObjectMap
      Adds a pair to the map (optional operation).

      This default implementation just delegates to the corresponding function method.

      Specified by:
      put in interface Function<K,​V>
      Specified by:
      put in interface Map<K,​V>
      Specified by:
      put in interface Object2ObjectFunction<K,​V>
      Specified by:
      put in interface Object2ObjectMap<K,​V>
      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.
      See Also:
      Function.put(Object,Object)

    • remove

      public V remove​(Object k)
      Description copied from interface: Object2ObjectMap
      Removes the mapping with the given key (optional operation).

      This default implementation just delegates to the corresponding type-specific–function method.

      Specified by:
      remove in interface Function<K,​V>
      Specified by:
      remove in interface Map<K,​V>
      Specified by:
      remove in interface Object2ObjectFunction<K,​V>
      Specified by:
      remove in interface Object2ObjectMap<K,​V>
      Parameters:
      k - the key.
      Returns:
      the old value, or the default return value if no value was present for the given key.
      See Also:
      Function.remove(Object)

    • get

      public V get​(Object k)
      Description copied from interface: Object2ObjectFunction
      Returns the value to which the given key is mapped.
      Specified by:
      get in interface Function<K,​V>
      Specified by:
      get in interface Map<K,​V>
      Specified by:
      get in interface Object2ObjectFunction<K,​V>
      Parameters:
      k - the key.
      Returns:
      the corresponding value, or the default return value if no value was present for the given key.
      See Also:
      Function.get(Object)

    • containsKey

      public boolean containsKey​(Object k)
      Description copied from interface: Object2ObjectMap
      Returns true if this function contains a mapping for the specified key.
      Specified by:
      containsKey in interface Function<K,​V>
      Specified by:
      containsKey in interface Map<K,​V>
      Specified by:
      containsKey in interface Object2ObjectMap<K,​V>
      Overrides:
      containsKey in class AbstractObject2ObjectMap<K,​V>
      Parameters:
      k - the key.
      Returns:
      true if this function associates a value to key.
      See Also:
      Map.containsKey(Object)

    • containsValue

      public boolean containsValue​(Object v)
      Specified by:
      containsValue in interface Map<K,​V>
      Overrides:
      containsValue in class AbstractObject2ObjectMap<K,​V>

    • clear

      public void clear()
      Description copied from interface: Object2ObjectMap
      Removes all of the mappings from this map (optional operation). The map will be empty after this call returns.
      Specified by:
      clear in interface Function<K,​V>
      Specified by:
      clear in interface Map<K,​V>
      Specified by:
      clear in interface Object2ObjectMap<K,​V>
      See Also:
      Map.clear()

    • size

      public int size()
      Description copied from interface: Object2ObjectMap
      Returns the number of key/value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
      Specified by:
      size in interface Function<K,​V>
      Specified by:
      size in interface Map<K,​V>
      Specified by:
      size in interface Object2ObjectMap<K,​V>
      Returns:
      the number of key-value mappings in this map.
      See Also:
      Size64

    • isEmpty

      public boolean isEmpty()
      Specified by:
      isEmpty in interface Map<K,​V>
      Overrides:
      isEmpty in class AbstractObject2ObjectMap<K,​V>

    • 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 Object2ObjectOpenHashMap<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.