Package it.unimi.dsi.fastutil.bytes

Class Byte2ObjectOpenCustomHashMap<V>

java.lang.Object
it.unimi.dsi.fastutil.bytes.AbstractByte2ObjectFunction<V>
it.unimi.dsi.fastutil.bytes.AbstractByte2ObjectMap<V>
it.unimi.dsi.fastutil.bytes.Byte2ObjectOpenCustomHashMap<V>
All Implemented Interfaces:
Byte2ObjectFunction<V>, Byte2ObjectMap<V>, Function<Byte,V>, Hash, Serializable, Cloneable, Function<Byte,V>, IntFunction<V>, Map<Byte,V>
public class Byte2ObjectOpenCustomHashMap<V> extends AbstractByte2ObjectMap<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.

Entries returned by the type-specific Byte2ObjectMap.entrySet() method implement the suitable type-specific Pair interface; only values are mutable.

See Also:

  • Constructor Details

    • Byte2ObjectOpenCustomHashMap

      public Byte2ObjectOpenCustomHashMap(int expected, float f, ByteHash.Strategy 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.

    • Byte2ObjectOpenCustomHashMap

      public Byte2ObjectOpenCustomHashMap(int expected, ByteHash.Strategy 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.

    • Byte2ObjectOpenCustomHashMap

      public Byte2ObjectOpenCustomHashMap(ByteHash.Strategy strategy)
      Creates a new hash map with initial expected Hash.DEFAULT_INITIAL_SIZE entries and Hash.DEFAULT_LOAD_FACTOR as load factor.
      Parameters:
      strategy - the strategy.

    • Byte2ObjectOpenCustomHashMap

      public Byte2ObjectOpenCustomHashMap(Map<? extends Byte,? extends V> m, float f, ByteHash.Strategy 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.

    • Byte2ObjectOpenCustomHashMap

      public Byte2ObjectOpenCustomHashMap(Map<? extends Byte,? extends V> m, ByteHash.Strategy 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.

    • Byte2ObjectOpenCustomHashMap

      public Byte2ObjectOpenCustomHashMap(Byte2ObjectMap<V> m, float f, ByteHash.Strategy 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.

    • Byte2ObjectOpenCustomHashMap

      public Byte2ObjectOpenCustomHashMap(Byte2ObjectMap<V> m, ByteHash.Strategy 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.

    • Byte2ObjectOpenCustomHashMap

      public Byte2ObjectOpenCustomHashMap(byte[] k, V[] v, float f, ByteHash.Strategy 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.

    • Byte2ObjectOpenCustomHashMap

      public Byte2ObjectOpenCustomHashMap(byte[] k, V[] v, ByteHash.Strategy 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 Details

    • strategy

      public ByteHash.Strategy strategy()
      Returns the hashing strategy.
      Returns:
      the hashing strategy of this custom hash map.

    • 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 Byte,? extends V> m)
      Description copied from class: AbstractByte2ObjectMap
      Specified by:
      putAll in interface Map<Byte,V>
      Overrides:
      putAll in class AbstractByte2ObjectMap<V>

    • put

      public V put(byte k, V v)
      Description copied from interface: Byte2ObjectFunction
      Adds a pair to the map (optional operation).
      Specified by:
      put in interface Byte2ObjectFunction<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:

    • remove

      public V remove(byte k)
      Description copied from interface: Byte2ObjectFunction
      Removes the mapping with the given key (optional operation).
      Specified by:
      remove in interface Byte2ObjectFunction<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:

    • get

      public V get(byte k)
      Description copied from interface: Byte2ObjectFunction
      Returns the value to which the given key is mapped.
      Specified by:
      get in interface Byte2ObjectFunction<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:

    • containsKey

      public boolean containsKey(byte k)
      Description copied from class: AbstractByte2ObjectMap
      Returns true if this function contains a mapping for the specified key.
      Specified by:
      containsKey in interface Byte2ObjectFunction<V>
      Specified by:
      containsKey in interface Byte2ObjectMap<V>
      Overrides:
      containsKey in class AbstractByte2ObjectMap<V>
      Parameters:
      k - the key.
      Returns:
      true if this function associates a value to key.
      See Also:

    • containsValue

      public boolean containsValue(Object v)
      Description copied from class: AbstractByte2ObjectMap
      Specified by:
      containsValue in interface Map<Byte,V>
      Overrides:
      containsValue in class AbstractByte2ObjectMap<V>

    • getOrDefault

      public V getOrDefault(byte k, V 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 Byte2ObjectFunction<V>
      Specified by:
      getOrDefault in interface Byte2ObjectMap<V>
      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 V putIfAbsent(byte k, V 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 Byte2ObjectMap<V>
      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(byte k, Object v)
      Removes the entry for the specified key only if it is currently mapped to the specified value.
      Specified by:
      remove in interface Byte2ObjectMap<V>
      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(byte k, V oldValue, V v)
      Replaces the entry for the specified key only if currently mapped to the specified value.
      Specified by:
      replace in interface Byte2ObjectMap<V>
      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 V replace(byte k, V v)
      Replaces the entry for the specified key only if it is currently mapped to some value.
      Specified by:
      replace in interface Byte2ObjectMap<V>
      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 V computeIfAbsent(byte k, IntFunction<? extends V> 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 Byte2ObjectMap<V>
      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 V computeIfAbsent(byte key, Byte2ObjectFunction<? extends V> 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 Byte2ObjectMap<V>
      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:

    • computeIfPresent

      public V computeIfPresent(byte k, BiFunction<? super Byte,? super V,? extends V> 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:
      computeIfPresent in interface Byte2ObjectMap<V>
      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:

    • compute

      public V compute(byte k, BiFunction<? super Byte,? super V,? extends V> 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:
      compute in interface Byte2ObjectMap<V>
      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 V merge(byte k, V v, BiFunction<? super V,? super V,? extends V> 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 Byte2ObjectMap<V>
      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: Byte2ObjectMap
      Removes all of the mappings from this map (optional operation). The map will be empty after this call returns.
      Specified by:
      clear in interface Byte2ObjectMap<V>
      Specified by:
      clear in interface Function<Byte,V>
      Specified by:
      clear in interface Map<Byte,V>
      See Also:

    • size

      public int size()
      Description copied from interface: Byte2ObjectMap
      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 Byte2ObjectMap<V>
      Specified by:
      size in interface Function<Byte,V>
      Specified by:
      size in interface Map<Byte,V>
      Returns:
      the number of key-value mappings in this map.
      See Also:

    • isEmpty

      public boolean isEmpty()
      Specified by:
      isEmpty in interface Map<Byte,V>
      Overrides:
      isEmpty in class AbstractByte2ObjectMap<V>

    • byte2ObjectEntrySet

      public Byte2ObjectMap.FastEntrySet<V> byte2ObjectEntrySet()
      Description copied from interface: Byte2ObjectMap
      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:
      byte2ObjectEntrySet in interface Byte2ObjectMap<V>
      Returns:
      a type-specific set view of the mappings contained in this map.
      See Also:

    • keySet

      public ByteSet keySet()
      Description copied from class: AbstractByte2ObjectMap
      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 Byte2ObjectMap<V>
      Specified by:
      keySet in interface Map<Byte,V>
      Overrides:
      keySet in class AbstractByte2ObjectMap<V>
      Returns:
      a set view of the keys of this map; it may be safely cast to a type-specific interface.
      See Also:

    • values

      public ObjectCollection<V> values()
      Description copied from class: AbstractByte2ObjectMap
      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 Byte2ObjectMap<V>
      Specified by:
      values in interface Map<Byte,V>
      Overrides:
      values in class AbstractByte2ObjectMap<V>
      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 Byte2ObjectOpenCustomHashMap<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<Byte,V>
      Overrides:
      hashCode in class AbstractByte2ObjectMap<V>
      Returns:
      a hash code for this map.