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Added in API level 1

public class

HashSet

extends AbstractSet<E>
implements Serializable Cloneable Set<E>

java.lang.Object
↳	java.util.AbstractCollection<E>
	↳	java.util.AbstractSet<E>
		↳	java.util.HashSet<E>

Known Direct Subclasses

LinkedHashSet<E>

Class Overview

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

Summary

Public Constructors
	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.

Public Methods
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`.

[Expand]

Inherited Methods

From class java.util.AbstractSet

From class java.util.AbstractCollection

boolean	add(E object) Attempts to add `object` to the contents of this `Collection` (optional).
boolean	addAll( Collection<? extends E> collection) Attempts to add all of the objects contained in `collection` to the contents of this `Collection` (optional).
void	clear() Removes all elements from this `Collection`, leaving it empty (optional).
boolean	contains( Object object) Tests whether this `Collection` contains the specified object.
boolean	containsAll( Collection<?> collection) Tests whether this `Collection` contains all objects contained in the specified `Collection`.
boolean	isEmpty() Returns if this `Collection` contains no elements.
abstract Iterator<E>	iterator() Returns an instance of `Iterator` that may be used to access the objects contained by this `Collection`.
boolean	remove( Object object) Removes one instance of the specified object from this `Collection` if one is contained (optional).
boolean	removeAll( Collection<?> collection) Removes all occurrences in this `Collection` of each object in the specified `Collection` (optional).
boolean	retainAll( Collection<?> collection) Removes all objects from this `Collection` that are not also found in the `Collection` passed (optional).
abstract int	size() Returns a count of how many objects this `Collection` contains.
<T> T[]	toArray(T[] contents) Returns an array containing all elements contained in this `Collection`.
Object[]	toArray() Returns a new array containing all elements contained in this `Collection`.
String	toString() Returns the string representation of this `Collection`.

From class java.lang.Object

Object	clone() Creates and returns a copy of this `Object`.
boolean	equals( Object o) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of `Class` that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait() Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object.
final void	wait(long millis, int nanos) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires.
final void	wait(long millis) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires.

From interface java.lang.Iterable

From interface java.util.Collection

abstract boolean	add(E object) Attempts to add `object` to the contents of this `Collection` (optional).
abstract boolean	addAll( Collection<? extends E> collection) Attempts to add all of the objects contained in `Collection` to the contents of this `Collection` (optional).
abstract void	clear() Removes all elements from this `Collection`, leaving it empty (optional).
abstract boolean	contains( Object object) Tests whether this `Collection` contains the specified object.
abstract boolean	containsAll( Collection<?> collection) Tests whether this `Collection` contains all objects contained in the specified `Collection`.
abstract boolean	equals( Object object) Compares the argument to the receiver, and returns true if they represent the same object using a class specific comparison.
abstract int	hashCode() Returns an integer hash code for the receiver.
abstract boolean	isEmpty() Returns if this `Collection` contains no elements.
abstract Iterator<E>	iterator() Returns an instance of `Iterator` that may be used to access the objects contained by this `Collection`.
abstract boolean	remove( Object object) Removes one instance of the specified object from this `Collection` if one is contained (optional).
abstract boolean	removeAll( Collection<?> collection) Removes all occurrences in this `Collection` of each object in the specified `Collection` (optional).
abstract boolean	retainAll( Collection<?> collection) Removes all objects from this `Collection` that are not also found in the `Collection` passed (optional).
abstract int	size() Returns a count of how many objects this `Collection` contains.
abstract <T> T[]	toArray(T[] array) Returns an array containing all elements contained in this `Collection`.
abstract Object[]	toArray() Returns a new array containing all elements contained in this `Collection`.

From interface java.util.Set

abstract boolean	add(E object) Adds the specified object to this set.
abstract boolean	addAll( Collection<? extends E> collection) Adds the objects in the specified collection which do not exist yet in this set.
abstract void	clear() Removes all elements from this set, leaving it empty.
abstract boolean	contains( Object object) Searches this set for the specified object.
abstract boolean	containsAll( Collection<?> collection) Searches this set for all objects in the specified collection.
abstract boolean	equals( Object object) Compares the specified object to this set, and returns true if they represent the same object using a class specific comparison.
abstract int	hashCode() Returns the hash code for this set.
abstract boolean	isEmpty() Returns true if this set has no elements.
abstract Iterator<E>	iterator() Returns an iterator on the elements of this set.
abstract boolean	remove( Object object) Removes the specified object from this set.
abstract boolean	removeAll( Collection<?> collection) Removes all objects in the specified collection from this set.
abstract boolean	retainAll( Collection<?> collection) Removes all objects from this set that are not contained in the specified collection.
abstract int	size() Returns the number of elements in this set.
abstract <T> T[]	toArray(T[] array) Returns an array containing all elements contained in this set.
abstract Object[]	toArray() Returns an array containing all elements contained in this set.

Public Constructors

public HashSet ()

Added in API level 1

Constructs a new empty instance of HashSet.

public HashSet (int capacity)

Added in API level 1

Constructs a new instance of HashSet with the specified capacity.

Parameters

capacity	the initial capacity of this `HashSet`.

public HashSet (int capacity, float loadFactor)

Added in API level 1

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

Parameters

capacity	the initial capacity.
loadFactor	the initial load factor.

public HashSet (Collection<? extends E> collection)

Added in API level 1

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

Parameters

collection	the collection of elements to add.

Public Methods

public boolean add (E object)

Added in API level 1

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

Parameters

object	the object to add.

Returns

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

public void clear ()

Added in API level 1

Removes all elements from this HashSet, leaving it empty.

public Object clone ()

Added in API level 1

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

Returns

a shallow copy of this HashSet.

public boolean contains (Object object)

Added in API level 1

Searches this HashSet for the specified object.

Parameters

object	the object to search for.

Returns

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

public boolean isEmpty ()

Added in API level 1

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

Returns

true if this HashSet has no elements, false otherwise.

public Iterator<E> iterator ()

Added in API level 1

Returns an Iterator on the elements of this HashSet.

Returns

an Iterator on the elements of this HashSet.

public boolean remove (Object object)

Added in API level 1

Removes the specified object from this HashSet.

Parameters

object	the object to remove.

Returns

true if the object was removed, false otherwise.

public int size ()

Added in API level 1

Returns the number of elements in this HashSet.

Returns

the number of elements in this HashSet.

information

No examples for this method.

Frequently called with: [Clear]

This example was provided by APIMiner.

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Exceptions

Errors

HashSet

Class Overview

Summary

Public Constructors

public HashSet ()

public HashSet (int capacity)

Parameters

public HashSet (int capacity, float loadFactor)

Parameters

public HashSet (Collection<? extends E> collection)

Parameters

Public Methods

public boolean add (E object)

Parameters

Returns

public void clear ()

See Also

public Object clone ()

Returns

See Also

public boolean contains (Object object)

Parameters

Returns

public boolean isEmpty ()

Returns

See Also

public Iterator<E> iterator ()

Returns

See Also

public boolean remove (Object object)

Parameters

Returns

public int size ()

Returns