it.unimi.dsi.fastutil.objects
Class ReferenceOpenHashSet

java.lang.Object
  extended byit.unimi.dsi.fastutil.objects.AbstractReferenceCollection
      extended byit.unimi.dsi.fastutil.objects.AbstractReferenceSet
          extended byit.unimi.dsi.fastutil.objects.ReferenceOpenHashSet
All Implemented Interfaces:
Cloneable, Collection, Hash, ReferenceCollection, ReferenceSet, Serializable, Set

public class ReferenceOpenHashSet
extends AbstractReferenceSet
implements Serializable, Cloneable, Hash, ReferenceSet

A type-specific hash set with with a fast, small-footprint implementation.

Instances of this class use a hash table to represent a set. The table is enlarged as needed when new entries are created, but it is never made smaller (even on a clear()). A family of trimming methods lets you control the size of the table; this is particularly useful if you reuse instances of this class.

The enlargement speed is controlled by the growth factor, a positive number. If the growth factor is p, then the table is enlarged each time roughly by a factor 2p/16. By default, p is Hash.DEFAULT_GROWTH_FACTOR, which means that the table is doubled at each enlargement, but one can easily set more or less aggressive policies by calling growthFactor(int) (note that the growth factor is not serialised: deserialised tables gets the default growth factor).

See Also:
Hash, HashCommon, Serialized Form

Field Summary
static long serialVersionUID
           
 
Fields inherited from interface it.unimi.dsi.fastutil.Hash
DEFAULT_GROWTH_FACTOR, DEFAULT_INITIAL_SIZE, DEFAULT_LOAD_FACTOR, FREE, OCCUPIED, PRIMES, REMOVED
 
Constructor Summary
ReferenceOpenHashSet()
          Creates a new hash set with Hash.DEFAULT_INITIAL_SIZE elements and Hash.DEFAULT_LOAD_FACTOR as load factor.
ReferenceOpenHashSet(Collection c)
          Creates a new hash set with Hash.DEFAULT_LOAD_FACTOR as load factor copying a given collection.
ReferenceOpenHashSet(Collection c, float f)
          Creates a new hash set copying a given collection.
ReferenceOpenHashSet(int n)
          Creates a new hash set with Hash.DEFAULT_LOAD_FACTOR as load factor.
ReferenceOpenHashSet(int n, float f)
          Creates a new hash set.
ReferenceOpenHashSet(Object[] a)
          Creates a new hash set with Hash.DEFAULT_LOAD_FACTOR as load factor copying the elements of an array.
ReferenceOpenHashSet(Object[] a, float f)
          Creates a new set copying the elements of an array.
ReferenceOpenHashSet(ObjectIterator i)
          Creates a new hash set with Hash.DEFAULT_LOAD_FACTOR as load factor using elements provided by a type-specific iterator.
ReferenceOpenHashSet(ObjectIterator i, float f)
          Creates a new hash set using elements provided by a type-specific iterator.
ReferenceOpenHashSet(ReferenceCollection c)
          Creates a new hash set with Hash.DEFAULT_LOAD_FACTOR as load factor copying a given type-specific collection.
ReferenceOpenHashSet(ReferenceCollection c, float f)
          Creates a new hash set copying a given type-specific collection.
 
Method Summary
 boolean add(Object k)
           
 void clear()
           
 Object clone()
          Returns a deep copy of this set.
 boolean contains(Object k)
           
 int growthFactor()
          Gets the growth factor.
 void growthFactor(int growthFactor)
          Sets the growth factor.
 int hashCode()
          Returns a hash code for this set.
 boolean isEmpty()
           
 ObjectIterator objectIterator()
          Returns a type-specific iterator on the collection.
 boolean rehash()
          Rehashes this set without changing the table size.
 boolean remove(Object k)
           
 int size()
           
 boolean trim()
          Rehashes this set, making the table as small as possible.
 boolean trim(int n)
          Rehashes this set if the table is too large.
 
Methods inherited from class it.unimi.dsi.fastutil.objects.AbstractReferenceSet
equals, iterator
 
Methods inherited from class it.unimi.dsi.fastutil.objects.AbstractReferenceCollection
addAll, containsAll, iterator, removeAll, retainAll, toArray, toArray, toString
 
Methods inherited from class java.lang.Object
getClass, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface java.util.Set
addAll, containsAll, equals, iterator, removeAll, retainAll, toArray, toArray
 

Field Detail

serialVersionUID

public static final long serialVersionUID
See Also:
Constant Field Values
Constructor Detail

ReferenceOpenHashSet

public ReferenceOpenHashSet(int n,
                            float f)
Creates a new hash set. The actual table size is the least available prime greater than n/f.

Parameters:
n - the expected number of elements in the hash set.
f - the load factor.
See Also:
Hash.PRIMES

ReferenceOpenHashSet

public ReferenceOpenHashSet(int n)
Creates a new hash set with Hash.DEFAULT_LOAD_FACTOR as load factor.

Parameters:
n - the expected number of elements in the hash set.

ReferenceOpenHashSet

public ReferenceOpenHashSet()
Creates a new hash set with Hash.DEFAULT_INITIAL_SIZE elements and Hash.DEFAULT_LOAD_FACTOR as load factor.


ReferenceOpenHashSet

public ReferenceOpenHashSet(Collection c,
                            float f)
Creates a new hash set copying a given collection.

Parameters:
c - a Collection to be copied into the new hash set.
f - the load factor.

ReferenceOpenHashSet

public ReferenceOpenHashSet(Collection c)
Creates a new hash set with Hash.DEFAULT_LOAD_FACTOR as load factor copying a given collection.

Parameters:
c - a Collection to be copied into the new hash set.

ReferenceOpenHashSet

public ReferenceOpenHashSet(ReferenceCollection c,
                            float f)
Creates a new hash set copying a given type-specific collection.

Parameters:
c - a type-specific collection to be copied into the new hash set.
f - the load factor.

ReferenceOpenHashSet

public ReferenceOpenHashSet(ReferenceCollection c)
Creates a new hash set with Hash.DEFAULT_LOAD_FACTOR as load factor copying a given type-specific collection.

Parameters:
c - a type-specific collection to be copied into the new hash set.

ReferenceOpenHashSet

public ReferenceOpenHashSet(ObjectIterator i,
                            float f)
Creates a new hash set using elements provided by a type-specific iterator.

Parameters:
i - a type-specific iterator whose elements will fill the set.
f - the load factor.

ReferenceOpenHashSet

public ReferenceOpenHashSet(ObjectIterator i)
Creates a new hash set with Hash.DEFAULT_LOAD_FACTOR as load factor using elements provided by a type-specific iterator.

Parameters:
i - a type-specific iterator whose elements will fill the set.

ReferenceOpenHashSet

public ReferenceOpenHashSet(Object[] a,
                            float f)
Creates a new set copying the elements of an array.

Parameters:
a - an array to be copied into the new hash set.
f - the load factor.

ReferenceOpenHashSet

public ReferenceOpenHashSet(Object[] a)
Creates a new hash set with Hash.DEFAULT_LOAD_FACTOR as load factor copying the elements of an array.

Parameters:
a - an array to be copied into the new hash set.
Method Detail

growthFactor

public void growthFactor(int growthFactor)
Sets the growth factor. Subsequent enlargements will increase the table size roughly by a multiplicative factor of 2p/16.

Parameters:
growthFactor - the new growth factor; it must be positive.

growthFactor

public int growthFactor()
Gets the growth factor.

Returns:
the growth factor of this set.

add

public boolean add(Object k)
Specified by:
add in interface Set
Overrides:
add in class AbstractReferenceCollection

remove

public boolean remove(Object k)
Specified by:
remove in interface Set
Overrides:
remove in class AbstractReferenceCollection

contains

public boolean contains(Object k)
Specified by:
contains in interface Set

clear

public void clear()
Specified by:
clear in interface Set

objectIterator

public ObjectIterator objectIterator()
Description copied from interface: ReferenceCollection
Returns a type-specific iterator on the collection.

The iterator returned by the Collection.iterator() method and by this method are identical; however, using this method you can save a type casting.

Specified by:
objectIterator in interface ReferenceCollection
See Also:
Collection.iterator()

rehash

public boolean rehash()
Rehashes this set without changing the table size.

This method should be called when the set underwent numerous deletions and insertions. In this case, free entries become rare, and unsuccessful searches require probing all entries. For reasonable load factors this method is linear in the number of entries. You will need as much additional free memory as that occupied by the table.

If you need to reduce the table siza to fit exactly this set, you must use trim().

Returns:
true if there was enough memory to rehash the set, false otherwise.
See Also:
trim()

trim

public boolean trim()
Rehashes this set, 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 optimise access speed (by collecting deleted entries) and size.

If the table size is already the minimum possible, this method does nothing. If you want to guarantee rehashing, use rehash().

Returns:
true if there was enough memory to trim the set.
See Also:
trim(int), rehash()

trim

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

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

This method is useful when reusing sets. Clearing a set leaves the table size untouched. If you are reusing a set 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 sets.

Parameters:
n - the threshold for the trimming.
Returns:
true if there was enough memory to trim the set.
See Also:
trim(), rehash()

size

public int size()
Specified by:
size in interface Set

isEmpty

public boolean isEmpty()
Specified by:
isEmpty in interface Set
Overrides:
isEmpty in class AbstractReferenceCollection

clone

public Object clone()
Returns a deep copy of this set.

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

Returns:
a deep copy of this set.

hashCode

public int hashCode()
Returns a hash code for this set. 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 Set
Overrides:
hashCode in class AbstractReferenceSet
Returns:
a hash code for this set.