Package java.util

Class HashSet<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractSet<E>

java.util.HashSet<E>

All Implemented Interfaces:

Serializable, Cloneable, Iterable<E>, Collection<E>, Set<E>

Direct Known Subclasses:

LinkedHashSet

public class HashSet<E>
extends AbstractSet<E>
implements Set<E>, Cloneable, Serializable

HashSet is an implementation of a Set. All optional operations (adding and removing) are supported. The elements can be any objects.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor	Description
HashSet()	Constructs a new empty instance of HashSet.
HashSet(int capacity)	Constructs a new instance of HashSet with the specified capacity.
HashSet(int capacity, float loadFactor)	Constructs a new instance of HashSet with the specified capacity and load factor.
HashSet(Collection<? extends E> collection)	Constructs a new instance of HashSet containing the unique elements in the specified collection.

Method Summary

Modifier and Type	Method	Description
boolean	add(E object)	Adds the specified object to this HashSet if not already present.
void	clear()	Removes all elements from this HashSet, leaving it empty.
Object	clone()	Returns a new HashSet with the same elements and size as this HashSet.
boolean	contains(Object object)	Searches this HashSet for the specified object.
boolean	isEmpty()	Returns true if this HashSet has no elements, false otherwise.
Iterator<E>	iterator()	Returns an Iterator on the elements of this HashSet.
boolean	remove(Object object)	Removes the specified object from this HashSet.
int	size()	Returns the number of elements in this HashSet.

Methods inherited from class java.util.AbstractSet

equals, hashCode, removeAll

Methods inherited from class java.util.AbstractCollection

addAll, containsAll, retainAll, toArray, toArray, toString

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Set

addAll, containsAll, equals, hashCode, removeAll, retainAll, toArray, toArray

Constructor Detail

HashSet

public HashSet()

Constructs a new empty instance of HashSet.

HashSet

public HashSet(int capacity)

Constructs a new instance of HashSet with the specified capacity.

Parameters:

capacity - the initial capacity of this HashSet.

HashSet

public HashSet(int capacity,
               float loadFactor)

Constructs a new instance of HashSet with the specified capacity and load factor.

Parameters:

capacity - the initial capacity.

loadFactor - the initial load factor.

HashSet

public HashSet(Collection<? extends E> collection)

Constructs a new instance of HashSet containing the unique elements in the specified collection.

Parameters:

collection - the collection of elements to add.

Method Detail

add

public boolean add(E object)

Adds the specified object to this HashSet if not already present.

Specified by:

add in interface Collection<E>

Specified by:

add in interface Set<E>

Overrides:

add in class AbstractCollection<E>

Parameters:

object - the object to add.

Returns:

true when this HashSet did not already contain the object, false otherwise

clear

public void clear()

Removes all elements from this HashSet, leaving it empty.

Specified by:

clear in interface Collection<E>

Specified by:

clear in interface Set<E>

Overrides:

clear in class AbstractCollection<E>

See Also:

isEmpty(), size()

clone

public Object clone()

Returns a new HashSet with the same elements and size as this HashSet.

Overrides:

clone in class Object

Returns:

a shallow copy of this HashSet.

See Also:

Cloneable

contains

public boolean contains(Object object)

Searches this HashSet for the specified object.

Specified by:

contains in interface Collection<E>

Specified by:

contains in interface Set<E>

Overrides:

contains in class AbstractCollection<E>

Parameters:

object - the object to search for.

Returns:

true if object is an element of this HashSet, false otherwise.

isEmpty

public boolean isEmpty()

Returns true if this HashSet has no elements, false otherwise.

Specified by:

isEmpty in interface Collection<E>

Specified by:

isEmpty in interface Set<E>

Overrides:

isEmpty in class AbstractCollection<E>

Returns:

true if this HashSet has no elements, false otherwise.

See Also:

size()

iterator

public Iterator<E> iterator()

Returns an Iterator on the elements of this HashSet.

Specified by:

iterator in interface Collection<E>

Specified by:

iterator in interface Iterable<E>

Specified by:

iterator in interface Set<E>

Specified by:

iterator in class AbstractCollection<E>

Returns:

an Iterator on the elements of this HashSet.

See Also:

Iterator

remove

public boolean remove(Object object)

Removes the specified object from this HashSet.

Specified by:

remove in interface Collection<E>

Specified by:

remove in interface Set<E>

Overrides:

remove in class AbstractCollection<E>

Parameters:

object - the object to remove.

Returns:

true if the object was removed, false otherwise.

size

public int size()

Returns the number of elements in this HashSet.

Specified by:

size in interface Collection<E>

Specified by:

size in interface Set<E>

Specified by:

size in class AbstractCollection<E>

Returns:

the number of elements in this HashSet.