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public class java.util.HashSet<A>

(source file: HashSet.java)
java.lang.Object
   |
   +----java.util.AbstractCollection<A>
           |
           +----java.util.AbstractSet<A>
                   |
                   +----java.util.HashSet<A>
The pure class interface. 
public class HashSet<A>
  extends AbstractSet<A>
  implements Set<A>, Cloneable, java.io.Serializable
This class implements the Set interface, backed by a hash table (actually a HashMap). It offers constant time performance for the basic operations (add, remove, contains and size), assuming the the hash function disperses the elements properly among the buckets. This Set does not permit the null element.

Note that this implementation is not synchronized. If multiple threads access a HashSet concurrently, and at least one of the threads modifies the HashSet, it must be synchronized externally. This is typically accomplished by synchronizing on some object that naturally encapsulates the HashSet. If no such object exists, the HashSet should be "wrapped" using the Collections.synchronizedSet method. This is best done at creation time, to prevent accidental unsynchronized access to the HashSet: 

	Set s = Collections.synchronizedSet(new HashSet(...));

The Iterators returned by HashSet's iterator method are fail-fast: if the HashSet is modified at any time after the Iterator is created, in any way except through the Iterator's own remove method, the Iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the Iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

See also:
Collection, Set, ArraySet, Collections.synchronizedSet, HashMap

Constuctor Index

O HashSet(int, float)
Constructs a new, empty HashSet; the backing HashMap has the specified initial capacity
O HashSet(int)
Constructs a new, empty HashSet; the backing HashMap has the specified initial capacity
O HashSet(Collection<A>)
Constructs a new HashSet containing the elements in the specified Collection
O HashSet()
Constructs a new, empty HashSet; the backing HashMap has default capacity and load factor.

Methods

O add(A)
Adds the specified element to this HashSet if it is not already present.
O clear()
Removes all of the elements from this HashSet.
O clone()
Returns a shallow copy of this HashSet
O contains(A)
Returns true if this HashSet contains the specified element.
O isEmpty()
Returns true if this HashSet contains no elements.
O iterator()
Returns an Iterator over the elements in this HashSet
O remove(A)
Removes the given element from this HashSet if it is present.
O size()
Returns the number of elements in this HashSet (its cardinality).

Constructors

O HashSet
public HashSet();
Constructs a new, empty HashSet; the backing HashMap has default capacity and load factor.

O HashSet

public HashSet(Collection<A> c);
Constructs a new HashSet containing the elements in the specified Collection. The capacity of the backing HashMap is twice the size of the specified Collection, and the default load factor is used.

Throws:
NullPointerException -if the specified collection or one of its elements is null.

O HashSet

public HashSet(int initialCapacity,
               float loadFactor);
Constructs a new, empty HashSet; the backing HashMap has the specified initial capacity and the specified load factor.

Parameters:
initialCapacity - the initial capacity of the hashtable.
loadFactor - a number between 0.0 and 1.0.
Throws:
IllegalArgumentException -if the initial capacity is less than or equal to zero, or if the load factor is less than or equal to zero.

O HashSet

public HashSet(int initialCapacity);
Constructs a new, empty HashSet; the backing HashMap has the specified initial capacity and default load factor.

Parameters:
initialCapacity - the initial capacity of the hashtable.
Throws:
IllegalArgumentException -if the initial capacity is less than or equal to zero, or if the load factor is less than or equal to zero.

Methods

O iterator
public Iterator<A> iterator();
Returns an Iterator over the elements in this HashSet. The elements are returned in no particular order.

Overrides:
iterator in class AbstractCollection
See also:
ConcurrentModificationException

O size

public int size();
Returns the number of elements in this HashSet (its cardinality).

Overrides:
size in class AbstractCollection

O isEmpty

public boolean isEmpty();
Returns true if this HashSet contains no elements.

Overrides:
isEmpty in class AbstractCollection

O contains

public boolean contains(A o);
Returns true if this HashSet contains the specified element.

Throws:
NullPointerException -if the specified element is null.
Overrides:
contains in class AbstractCollection

O add

public boolean add(A o);
Adds the specified element to this HashSet if it is not already present.

Parameters:
o - element to be added to this HashSet.
Returns:
true if the HashSet did not already contain the specified element.
Throws:
NullPointerException -if the specified element is null.
Overrides:
add in class AbstractCollection

O remove

public boolean remove(A o);
Removes the given element from this HashSet if it is present.

Parameters:
o - object to be removed from this HashSet, if present.
Returns:
true if the HashSet contained the specified element.
Throws:
NullPointerException -if the specified element is null.
Overrides:
remove in class AbstractCollection

O clear

public void clear();
Removes all of the elements from this HashSet.

Overrides:
clear in class AbstractCollection

O clone

public Object clone();
Returns a shallow copy of this HashSet. (The elements themselves are not cloned.)

Overrides:
clone in class Object

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