Package it.unimi.dsi.fastutil.objects

Class Reference2IntOpenHashMap<K>

java.lang.Object
it.unimi.dsi.fastutil.objects.AbstractReference2IntFunction<K>
it.unimi.dsi.fastutil.objects.AbstractReference2IntMap<K>
it.unimi.dsi.fastutil.objects.Reference2IntOpenHashMap<K>
All Implemented Interfaces:
Function<K,Integer>, Hash, Reference2IntFunction<K>, Reference2IntMap<K>, Serializable, Cloneable, Function<K,Integer>, ToIntFunction<K>, Map<K,Integer>
public class Reference2IntOpenHashMap<K> extends AbstractReference2IntMap<K> 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.

Entries returned by the type-specific Reference2IntMap.entrySet() method implement the suitable type-specific Pair interface; only values are mutable.

See Also:

  • Constructor Details

    • Reference2IntOpenHashMap

      public Reference2IntOpenHashMap(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.

    • Reference2IntOpenHashMap

      public Reference2IntOpenHashMap(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.

    • Reference2IntOpenHashMap

      public Reference2IntOpenHashMap()
      Creates a new hash map with initial expected Hash.DEFAULT_INITIAL_SIZE entries and Hash.DEFAULT_LOAD_FACTOR as load factor.

    • Reference2IntOpenHashMap

      public Reference2IntOpenHashMap(Map<? extends K,? extends Integer> 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.

    • Reference2IntOpenHashMap

      public Reference2IntOpenHashMap(Map<? extends K,? extends Integer> 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.

    • Reference2IntOpenHashMap

      public Reference2IntOpenHashMap(Reference2IntMap<K> 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.

    • Reference2IntOpenHashMap

      public Reference2IntOpenHashMap(Reference2IntMap<K> 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.

    • Reference2IntOpenHashMap

      public Reference2IntOpenHashMap(K[] k, int[] 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.

    • Reference2IntOpenHashMap

      public Reference2IntOpenHashMap(K[] k, int[] 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

    • ensureCapacity

      public void ensureCapacity(int capacity)
      Ensures that this map can hold a certain number of keys without rehashing.
      Parameters:
      capacity - a number of keys; there will be no rehashing unless the map size exceeds this number.

    • putAll

      public void putAll(Map<? extends K,? extends Integer> m)
      Description copied from class: AbstractReference2IntMap
      Specified by:
      putAll in interface Map<K,Integer>
      Overrides:
      putAll in class AbstractReference2IntMap<K>

    • put

      public int put(K k, int v)
      Description copied from interface: Reference2IntFunction
      Adds a pair to the map (optional operation).
      Specified by:
      put in interface Reference2IntFunction<K>
      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:

    • addTo

      public int addTo(K k, int incr)
      Adds an increment to value currently associated with a key.

      Note that this method respects the default return value semantics: when called with a key that does not currently appears in the map, the key will be associated with the default return value plus the given increment.

      Parameters:
      k - the key.
      incr - the increment.
      Returns:
      the old value, or the default return value if no value was present for the given key.

    • removeInt

      public int removeInt(Object k)
      Description copied from interface: Reference2IntFunction
      Removes the mapping with the given key (optional operation).
      Specified by:
      removeInt in interface Reference2IntFunction<K>
      Parameters:
      k - the key.
      Returns:
      the old value, or the default return value if no value was present for the given key.
      See Also:

    • getInt

      public int getInt(Object k)
      Description copied from interface: Reference2IntFunction
      Returns the value to which the given key is mapped.
      Specified by:
      getInt in interface Reference2IntFunction<K>
      Parameters:
      k - the key.
      Returns:
      the corresponding value, or the default return value if no value was present for the given key.
      See Also:

    • containsKey

      public boolean containsKey(Object k)
      Description copied from class: AbstractReference2IntMap
      Returns true if this function contains a mapping for the specified key.
      Specified by:
      containsKey in interface Function<K,Integer>
      Specified by:
      containsKey in interface Map<K,Integer>
      Specified by:
      containsKey in interface Reference2IntMap<K>
      Overrides:
      containsKey in class AbstractReference2IntMap<K>
      Parameters:
      k - the key.
      Returns:
      true if this function associates a value to key.
      See Also:

    • containsValue

      public boolean containsValue(int v)
      Description copied from class: AbstractReference2IntMap
      Returns true if this map maps one or more keys to the specified value.
      Specified by:
      containsValue in interface Reference2IntMap<K>
      Overrides:
      containsValue in class AbstractReference2IntMap<K>
      See Also:

    • getOrDefault

      public int getOrDefault(Object k, int defaultValue)
      Returns the value to which the specified key is mapped, or the defaultValue if this map contains no mapping for the key.
      Specified by:
      getOrDefault in interface Reference2IntFunction<K>
      Specified by:
      getOrDefault in interface Reference2IntMap<K>
      Parameters:
      k - the key.
      defaultValue - the default mapping of the key.
      Returns:
      the value to which the specified key is mapped, or the defaultValue if this map contains no mapping for the key.
      See Also:

    • putIfAbsent

      public int putIfAbsent(K k, int v)
      If the specified key is not already associated with a value, associates it with the given value and returns the default return value, else returns the current value.
      Specified by:
      putIfAbsent in interface Reference2IntMap<K>
      Parameters:
      k - key with which the specified value is to be associated.
      v - value to be associated with the specified key.
      Returns:
      the previous value associated with the specified key, or the default return value if there was no mapping for the key.
      See Also:

    • remove

      public boolean remove(Object k, int v)
      Removes the entry for the specified key only if it is currently mapped to the specified value.
      Specified by:
      remove in interface Reference2IntMap<K>
      Parameters:
      k - key with which the specified value is associated.
      v - value expected to be associated with the specified key.
      Returns:
      true if the value was removed.
      See Also:

    • replace

      public boolean replace(K k, int oldValue, int v)
      Replaces the entry for the specified key only if currently mapped to the specified value.
      Specified by:
      replace in interface Reference2IntMap<K>
      Parameters:
      k - key with which the specified value is associated.
      oldValue - value expected to be associated with the specified key.
      v - value to be associated with the specified key.
      Returns:
      true if the value was replaced.
      See Also:

    • replace

      public int replace(K k, int v)
      Replaces the entry for the specified key only if it is currently mapped to some value.
      Specified by:
      replace in interface Reference2IntMap<K>
      Parameters:
      k - key with which the specified value is associated.
      v - value to be associated with the specified key.
      Returns:
      the previous value associated with the specified key, or the default return value if there was no mapping for the key.
      See Also:

    • computeIfAbsent

      public int computeIfAbsent(K k, ToIntFunction<? super K> mappingFunction)
      If the specified key is not already associated with a value, attempts to compute its value using the given mapping function and enters it into this map.

      Note that contrarily to the default computeIfAbsent(), it is not possible to not add a value for a given key, since the mappingFunction cannot return null. If such a behavior is needed, please use the corresponding nullable version.

      Specified by:
      computeIfAbsent in interface Reference2IntMap<K>
      Parameters:
      k - key with which the specified value is to be associated.
      mappingFunction - the function to compute a value.
      Returns:
      the current (existing or computed) value associated with the specified key.
      See Also:

    • computeIfAbsent

      public int computeIfAbsent(K key, Reference2IntFunction<? super K> mappingFunction)
      If the specified key is not already associated with a value, attempts to compute its value using the given mapping function and enters it into this map, unless the key is not present in the given mapping function.

      This version of computeIfAbsent() uses a type-specific version of fastutil's Function. Since Function has a containsKey() method, it is possible to avoid adding a key by having containsKey() return false for that key.

      Specified by:
      computeIfAbsent in interface Reference2IntMap<K>
      Parameters:
      key - key with which the specified value is to be associated.
      mappingFunction - the function to compute a value.
      Returns:
      the current (existing or computed) value associated with the specified key.
      See Also:

    • computeIntIfPresent

      public int computeIntIfPresent(K k, BiFunction<? super K,? super Integer,? extends Integer> remappingFunction)
      If the value for the specified key is present, attempts to compute a new mapping given the key and its current mapped value.
      Specified by:
      computeIntIfPresent in interface Reference2IntMap<K>
      Parameters:
      k - key with which the specified value is to be associated.
      remappingFunction - the function to compute a value.
      Returns:
      the new value associated with the specified key, or the default return value if none.
      See Also:

    • computeInt

      public int computeInt(K k, BiFunction<? super K,? super Integer,? extends Integer> remappingFunction)
      Attempts to compute a mapping for the specified key and its current mapped value (or null if there is no current mapping).

      If the function returns null, the mapping is removed (or remains absent if initially absent). If the function itself throws an (unchecked) exception, the exception is rethrown, and the current mapping is left unchanged.

      Specified by:
      computeInt in interface Reference2IntMap<K>
      Parameters:
      k - key with which the specified value is to be associated.
      remappingFunction - the function to compute a value.
      Returns:
      the new value associated with the specified key, or the default return value if none.
      See Also:

    • merge

      public int merge(K k, int v, BiFunction<? super Integer,? super Integer,? extends Integer> remappingFunction)
      If the specified key is not already associated with a value, associates it with the given value. Otherwise, replaces the associated value with the results of the given remapping function, or removes if the result is null.
      Specified by:
      merge in interface Reference2IntMap<K>
      Parameters:
      k - key with which the resulting value is to be associated.
      v - the value to be merged with the existing value associated with the key or, if no existing value is associated with the key, to be associated with the key.
      remappingFunction - the function to recompute a value if present.
      Returns:
      the new value associated with the specified key, or the default return value if no value is associated with the key.
      See Also:

    • clear

      public void clear()
      Description copied from interface: Reference2IntMap
      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,Integer>
      Specified by:
      clear in interface Map<K,Integer>
      Specified by:
      clear in interface Reference2IntMap<K>
      See Also:

    • size

      public int size()
      Description copied from interface: Reference2IntMap
      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,Integer>
      Specified by:
      size in interface Map<K,Integer>
      Specified by:
      size in interface Reference2IntMap<K>
      Returns:
      the number of key-value mappings in this map.
      See Also:

    • isEmpty

      public boolean isEmpty()
      Specified by:
      isEmpty in interface Map<K,Integer>
      Overrides:
      isEmpty in class AbstractReference2IntMap<K>

    • reference2IntEntrySet

      public Reference2IntMap.FastEntrySet<K> reference2IntEntrySet()
      Description copied from interface: Reference2IntMap
      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:
      reference2IntEntrySet in interface Reference2IntMap<K>
      Returns:
      a type-specific set view of the mappings contained in this map.
      See Also:

    • keySet

      public ReferenceSet<K> keySet()
      Description copied from class: AbstractReference2IntMap
      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,Integer>
      Specified by:
      keySet in interface Reference2IntMap<K>
      Overrides:
      keySet in class AbstractReference2IntMap<K>
      Returns:
      a set view of the keys of this map; it may be safely cast to a type-specific interface.
      See Also:

    • values

      public IntCollection values()
      Description copied from class: AbstractReference2IntMap
      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,Integer>
      Specified by:
      values in interface Reference2IntMap<K>
      Overrides:
      values in class AbstractReference2IntMap<K>
      Returns:
      a set view of the values of this map; it may be safely cast to a type-specific interface.
      See Also:

    • 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

      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:

    • clone

      public Reference2IntOpenHashMap<K> 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,Integer>
      Overrides:
      hashCode in class AbstractReference2IntMap<K>
      Returns:
      a hash code for this map.