E - the type of elements maintained by this setpublic class HashSet<E> extends AbstractSet<E> implements Set<E>, Cloneable, Serializable
Set interface, backed by a hash table
(actually a HashMap instance). It makes no guarantees as to the
iteration order of the set; in particular, it does not guarantee that the
order will remain constant over time. This class permits the null
element.
This class offers constant time performance for the basic operations
(add, remove, contains and size),
assuming the hash function disperses the elements properly among the
buckets. Iterating over this set requires time proportional to the sum of
the HashSet instance's size (the number of elements) plus the
"capacity" of the backing HashMap instance (the number of
buckets). Thus, it's very important not to set the initial capacity too
high (or the load factor too low) if iteration performance is important.
Note that this implementation is not synchronized.
If multiple threads access a hash set concurrently, and at least one of
the threads modifies the set, it must be synchronized externally.
This is typically accomplished by synchronizing on some object that
naturally encapsulates the set.
If no such object exists, the set should be "wrapped" using the
Collections.synchronizedSet
method. This is best done at creation time, to prevent accidental
unsynchronized access to the set:
Set s = Collections.synchronizedSet(new HashSet(...));
The iterators returned by this class's iterator method are
fail-fast: if the set is modified at any time after the iterator is
created, in any way except through the iterator's own remove
method, the Iterator throws 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.
Note that the fail-fast behavior of an iterator cannot be guaranteed
as it is, generally speaking, impossible to make any hard guarantees in the
presence of unsynchronized concurrent modification. Fail-fast iterators
throw ConcurrentModificationException on a best-effort basis.
Therefore, it would be wrong to write a program that depended on this
exception for its correctness: the fail-fast behavior of iterators
should be used only to detect bugs.
This class is a member of the Java Collections Framework.
Collection,
Set,
TreeSet,
HashMap,
Serialized Form| Constructor and Description |
|---|
HashSet()
Constructs a new, empty set; the backing
HashMap instance has
default initial capacity (16) and load factor (0.75). |
HashSet(Collection<? extends E> c)
Constructs a new set containing the elements in the specified
collection.
|
HashSet(int initialCapacity)
Constructs a new, empty set; the backing
HashMap instance has
the specified initial capacity and default load factor (0.75). |
HashSet(int initialCapacity,
float loadFactor)
Constructs a new, empty set; the backing
HashMap instance has
the specified initial capacity and the specified load factor. |
| Modifier and Type | Method and Description |
|---|---|
boolean |
add(E e)
Adds the specified element to this set if it is not already present.
|
void |
clear()
Removes all of the elements from this set.
|
Object |
clone()
Returns a shallow copy of this
HashSet instance: the elements
themselves are not cloned. |
boolean |
contains(Object o)
Returns
true if this set contains the specified element. |
boolean |
isEmpty()
Returns
true if this set contains no elements. |
Iterator<E> |
iterator()
Returns an iterator over the elements in this set.
|
boolean |
remove(Object o)
Removes the specified element from this set if it is present.
|
int |
size()
Returns the number of elements in this set (its cardinality).
|
Spliterator<E> |
spliterator()
Creates a late-binding
and fail-fast
Spliterator over the elements in this
set. |
equals, hashCode, removeAlladdAll, containsAll, retainAll, toArray, toArray, toStringfinalize, getClass, notify, notifyAll, wait, wait, waitaddAll, containsAll, equals, hashCode, of, of, of, of, of, of, of, of, of, of, of, of, removeAll, retainAll, toArray, toArrayparallelStream, removeIf, streampublic HashSet()
HashMap instance has
default initial capacity (16) and load factor (0.75).public HashSet(Collection<? extends E> c)
HashMap is created with default load factor
(0.75) and an initial capacity sufficient to contain the elements in
the specified collection.c - the collection whose elements are to be placed into this setNullPointerException - if the specified collection is nullpublic HashSet(int initialCapacity,
float loadFactor)
HashMap instance has
the specified initial capacity and the specified load factor.initialCapacity - the initial capacity of the hash maploadFactor - the load factor of the hash mapIllegalArgumentException - if the initial capacity is less
than zero, or if the load factor is nonpositivepublic HashSet(int initialCapacity)
HashMap instance has
the specified initial capacity and default load factor (0.75).initialCapacity - the initial capacity of the hash tableIllegalArgumentException - if the initial capacity is less
than zeropublic Iterator<E> iterator()
iterator in interface Iterable<E>iterator in interface Collection<E>iterator in interface Set<E>iterator in class AbstractCollection<E>ConcurrentModificationExceptionpublic int size()
size in interface Collection<E>size in interface Set<E>size in class AbstractCollection<E>public boolean isEmpty()
true if this set contains no elements.isEmpty in interface Collection<E>isEmpty in interface Set<E>isEmpty in class AbstractCollection<E>true if this set contains no elementspublic boolean contains(Object o)
true if this set contains the specified element.
More formally, returns true if and only if this set
contains an element e such that
Objects.equals(o, e).contains in interface Collection<E>contains in interface Set<E>contains in class AbstractCollection<E>o - element whose presence in this set is to be testedtrue if this set contains the specified elementpublic boolean add(E e)
e to this set if
this set contains no element e2 such that
Objects.equals(e, e2).
If this set already contains the element, the call leaves the set
unchanged and returns false.add in interface Collection<E>add in interface Set<E>add in class AbstractCollection<E>e - element to be added to this settrue if this set did not already contain the specified
elementpublic boolean remove(Object o)
e such that
Objects.equals(o, e),
if this set contains such an element. Returns true if
this set contained the element (or equivalently, if this set
changed as a result of the call). (This set will not contain the
element once the call returns.)remove in interface Collection<E>remove in interface Set<E>remove in class AbstractCollection<E>o - object to be removed from this set, if presenttrue if the set contained the specified elementpublic void clear()
clear in interface Collection<E>clear in interface Set<E>clear in class AbstractCollection<E>public Object clone()
HashSet instance: the elements
themselves are not cloned.public Spliterator<E> spliterator()
Spliterator over the elements in this
set.
The Spliterator reports Spliterator.SIZED and
Spliterator.DISTINCT. Overriding implementations should document
the reporting of additional characteristic values.
spliterator in interface Iterable<E>spliterator in interface Collection<E>spliterator in interface Set<E>Spliterator over the elements in this set Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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DRAFT 9-internal+0-2016-01-26-133437.ivan.openjdk9onspinwait