E - the type of elements maintained by this setpublic interface Set<E> extends Collection<E>
e1 and e2 such that
e1.equals(e2), and at most one null element. As implied by
its name, this interface models the mathematical set abstraction.
The Set interface places additional stipulations, beyond those
inherited from the Collection interface, on the contracts of all
constructors and on the contracts of the add, equals and
hashCode methods. Declarations for other inherited methods are
also included here for convenience. (The specifications accompanying these
declarations have been tailored to the Set interface, but they do
not contain any additional stipulations.)
The additional stipulation on constructors is, not surprisingly, that all constructors must create a set that contains no duplicate elements (as defined above).
Note: Great care must be exercised if mutable objects are used as set
elements. The behavior of a set is not specified if the value of an object
is changed in a manner that affects equals comparisons while the
object is an element in the set. A special case of this prohibition is
that it is not permissible for a set to contain itself as an element.
Some set implementations have restrictions on the elements that
they may contain. For example, some implementations prohibit null elements,
and some have restrictions on the types of their elements. Attempting to
add an ineligible element throws an unchecked exception, typically
NullPointerException or ClassCastException. Attempting
to query the presence of an ineligible element may throw an exception,
or it may simply return false; some implementations will exhibit the former
behavior and some will exhibit the latter. More generally, attempting an
operation on an ineligible element whose completion would not result in
the insertion of an ineligible element into the set may throw an
exception or it may succeed, at the option of the implementation.
Such exceptions are marked as "optional" in the specification for this
interface.
The Set.of() static factory methods
provide a convenient way to create immutable sets. The Set
instances created by these methods have the following characteristics:
UnsupportedOperationException.
However, if the contained elements are themselves mutable, this may cause the
Set to behave inconsistently or its contents to appear to change.
null elements. Attempts to create them with
null elements result in NullPointerException.
IllegalArgumentException.
==),
identity hash code, and synchronization) are unreliable and should be avoided.
This interface is a member of the Java Collections Framework.
Collection,
List,
SortedSet,
HashSet,
TreeSet,
AbstractSet,
Collections.singleton(java.lang.Object),
Collections.EMPTY_SET| Modifier and Type | Method and Description |
|---|---|
boolean |
add(E e)
Adds the specified element to this set if it is not already present
(optional operation).
|
boolean |
addAll(Collection<? extends E> c)
Adds all of the elements in the specified collection to this set if
they're not already present (optional operation).
|
void |
clear()
Removes all of the elements from this set (optional operation).
|
boolean |
contains(Object o)
Returns
true if this set contains the specified element. |
boolean |
containsAll(Collection<?> c)
Returns
true if this set contains all of the elements of the
specified collection. |
boolean |
equals(Object o)
Compares the specified object with this set for equality.
|
int |
hashCode()
Returns the hash code value for this set.
|
boolean |
isEmpty()
Returns
true if this set contains no elements. |
Iterator<E> |
iterator()
Returns an iterator over the elements in this set.
|
static <E> Set<E> |
of()
Returns an immutable set containing zero elements.
|
static <E> Set<E> |
of(E... elements)
Returns an immutable set containing an arbitrary number of elements.
|
static <E> Set<E> |
of(E e1)
Returns an immutable set containing one element.
|
static <E> Set<E> |
of(E e1,
E e2)
Returns an immutable set containing two elements.
|
static <E> Set<E> |
of(E e1,
E e2,
E e3)
Returns an immutable set containing three elements.
|
static <E> Set<E> |
of(E e1,
E e2,
E e3,
E e4)
Returns an immutable set containing four elements.
|
static <E> Set<E> |
of(E e1,
E e2,
E e3,
E e4,
E e5)
Returns an immutable set containing five elements.
|
static <E> Set<E> |
of(E e1,
E e2,
E e3,
E e4,
E e5,
E e6)
Returns an immutable set containing six elements.
|
static <E> Set<E> |
of(E e1,
E e2,
E e3,
E e4,
E e5,
E e6,
E e7)
Returns an immutable set containing seven elements.
|
static <E> Set<E> |
of(E e1,
E e2,
E e3,
E e4,
E e5,
E e6,
E e7,
E e8)
Returns an immutable set containing eight elements.
|
static <E> Set<E> |
of(E e1,
E e2,
E e3,
E e4,
E e5,
E e6,
E e7,
E e8,
E e9)
Returns an immutable set containing nine elements.
|
static <E> Set<E> |
of(E e1,
E e2,
E e3,
E e4,
E e5,
E e6,
E e7,
E e8,
E e9,
E e10)
Returns an immutable set containing ten elements.
|
boolean |
remove(Object o)
Removes the specified element from this set if it is present
(optional operation).
|
boolean |
removeAll(Collection<?> c)
Removes from this set all of its elements that are contained in the
specified collection (optional operation).
|
boolean |
retainAll(Collection<?> c)
Retains only the elements in this set that are contained in the
specified collection (optional operation).
|
int |
size()
Returns the number of elements in this set (its cardinality).
|
default Spliterator<E> |
spliterator()
Creates a
Spliterator over the elements in this set. |
Object[] |
toArray()
Returns an array containing all of the elements in this set.
|
<T> T[] |
toArray(T[] a)
Returns an array containing all of the elements in this set; the
runtime type of the returned array is that of the specified array.
|
parallelStream, removeIf, streamint size()
Integer.MAX_VALUE elements, returns
Integer.MAX_VALUE.size in interface Collection<E>boolean isEmpty()
true if this set contains no elements.isEmpty in interface Collection<E>true if this set contains no elementsboolean 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>o - element whose presence in this set is to be testedtrue if this set contains the specified elementClassCastException - if the type of the specified element
is incompatible with this set
(optional)NullPointerException - if the specified element is null and this
set does not permit null elements
(optional)Iterator<E> iterator()
Object[] toArray()
The returned array will be "safe" in that no references to it are maintained by this set. (In other words, this method must allocate a new array even if this set is backed by an array). The caller is thus free to modify the returned array.
This method acts as bridge between array-based and collection-based APIs.
toArray in interface Collection<E><T> T[] toArray(T[] a)
If this set fits in the specified array with room to spare
(i.e., the array has more elements than this set), the element in
the array immediately following the end of the set is set to
null. (This is useful in determining the length of this
set only if the caller knows that this set does not contain
any null elements.)
If this set makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.
Like the toArray() method, this method acts as bridge between
array-based and collection-based APIs. Further, this method allows
precise control over the runtime type of the output array, and may,
under certain circumstances, be used to save allocation costs.
Suppose x is a set known to contain only strings.
The following code can be used to dump the set into a newly allocated
array of String:
String[] y = x.toArray(new String[0]);
Note that toArray(new Object[0]) is identical in function to
toArray().toArray in interface Collection<E>T - the runtime type of the array to contain the collectiona - the array into which the elements of this set are to be
stored, if it is big enough; otherwise, a new array of the same
runtime type is allocated for this purpose.ArrayStoreException - if the runtime type of the specified array
is not a supertype of the runtime type of every element in this
setNullPointerException - if the specified array is nullboolean add(E e)
e to this set if the 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. In combination with the
restriction on constructors, this ensures that sets never contain
duplicate elements.
The stipulation above does not imply that sets must accept all
elements; sets may refuse to add any particular element, including
null, and throw an exception, as described in the
specification for Collection.add.
Individual set implementations should clearly document any
restrictions on the elements that they may contain.
add in interface Collection<E>e - element to be added to this settrue if this set did not already contain the specified
elementUnsupportedOperationException - if the add operation
is not supported by this setClassCastException - if the class of the specified element
prevents it from being added to this setNullPointerException - if the specified element is null and this
set does not permit null elementsIllegalArgumentException - if some property of the specified element
prevents it from being added to this setboolean 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>o - object to be removed from this set, if presenttrue if this set contained the specified elementClassCastException - if the type of the specified element
is incompatible with this set
(optional)NullPointerException - if the specified element is null and this
set does not permit null elements
(optional)UnsupportedOperationException - if the remove operation
is not supported by this setboolean containsAll(Collection<?> c)
true if this set contains all of the elements of the
specified collection. If the specified collection is also a set, this
method returns true if it is a subset of this set.containsAll in interface Collection<E>c - collection to be checked for containment in this settrue if this set contains all of the elements of the
specified collectionClassCastException - if the types of one or more elements
in the specified collection are incompatible with this
set
(optional)NullPointerException - if the specified collection contains one
or more null elements and this set does not permit null
elements
(optional),
or if the specified collection is nullcontains(Object)boolean addAll(Collection<? extends E> c)
addAll operation effectively
modifies this set so that its value is the union of the two
sets. The behavior of this operation is undefined if the specified
collection is modified while the operation is in progress.addAll in interface Collection<E>c - collection containing elements to be added to this settrue if this set changed as a result of the callUnsupportedOperationException - if the addAll operation
is not supported by this setClassCastException - if the class of an element of the
specified collection prevents it from being added to this setNullPointerException - if the specified collection contains one
or more null elements and this set does not permit null
elements, or if the specified collection is nullIllegalArgumentException - if some property of an element of the
specified collection prevents it from being added to this setadd(Object)boolean retainAll(Collection<?> c)
retainAll in interface Collection<E>c - collection containing elements to be retained in this settrue if this set changed as a result of the callUnsupportedOperationException - if the retainAll operation
is not supported by this setClassCastException - if the class of an element of this set
is incompatible with the specified collection
(optional)NullPointerException - if this set contains a null element and the
specified collection does not permit null elements
(optional),
or if the specified collection is nullremove(Object)boolean removeAll(Collection<?> c)
removeAll in interface Collection<E>c - collection containing elements to be removed from this settrue if this set changed as a result of the callUnsupportedOperationException - if the removeAll operation
is not supported by this setClassCastException - if the class of an element of this set
is incompatible with the specified collection
(optional)NullPointerException - if this set contains a null element and the
specified collection does not permit null elements
(optional),
or if the specified collection is nullremove(Object),
contains(Object)void clear()
clear in interface Collection<E>UnsupportedOperationException - if the clear method
is not supported by this setboolean equals(Object o)
true if the specified object is also a set, the two sets
have the same size, and every member of the specified set is
contained in this set (or equivalently, every member of this set is
contained in the specified set). This definition ensures that the
equals method works properly across different implementations of the
set interface.equals in interface Collection<E>equals in class Objecto - object to be compared for equality with this settrue if the specified object is equal to this setObject.hashCode(),
HashMapint hashCode()
null element is defined to be zero.
This ensures that s1.equals(s2) implies that
s1.hashCode()==s2.hashCode() for any two sets s1
and s2, as required by the general contract of
Object.hashCode().hashCode in interface Collection<E>hashCode in class ObjectObject.equals(Object),
equals(Object)default Spliterator<E> spliterator()
Spliterator over the elements in this set.
The Spliterator reports Spliterator.DISTINCT.
Implementations should document the reporting of additional
characteristic values.
spliterator in interface Collection<E>spliterator in interface Iterable<E>Iterator. The spliterator inherits the
fail-fast properties of the set's iterator.
The created Spliterator additionally reports
Spliterator.SIZED.
Spliterator additionally reports
Spliterator.SUBSIZED.Spliterator over the elements in this setstatic <E> Set<E> of()
E - the Set's element typeSetstatic <E> Set<E> of(E e1)
E - the Set's element typee1 - the single elementSet containing the specified elementNullPointerException - if the element is nullstatic <E> Set<E> of(E e1, E e2)
E - the Set's element typee1 - the first elemente2 - the second elementSet containing the specified elementsIllegalArgumentException - if the elements are duplicatesNullPointerException - if an element is nullstatic <E> Set<E> of(E e1, E e2, E e3)
E - the Set's element typee1 - the first elemente2 - the second elemente3 - the third elementSet containing the specified elementsIllegalArgumentException - if there are any duplicate elementsNullPointerException - if an element is nullstatic <E> Set<E> of(E e1, E e2, E e3, E e4)
E - the Set's element typee1 - the first elemente2 - the second elemente3 - the third elemente4 - the fourth elementSet containing the specified elementsIllegalArgumentException - if there are any duplicate elementsNullPointerException - if an element is nullstatic <E> Set<E> of(E e1, E e2, E e3, E e4, E e5)
E - the Set's element typee1 - the first elemente2 - the second elemente3 - the third elemente4 - the fourth elemente5 - the fifth elementSet containing the specified elementsIllegalArgumentException - if there are any duplicate elementsNullPointerException - if an element is nullstatic <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6)
E - the Set's element typee1 - the first elemente2 - the second elemente3 - the third elemente4 - the fourth elemente5 - the fifth elemente6 - the sixth elementSet containing the specified elementsIllegalArgumentException - if there are any duplicate elementsNullPointerException - if an element is nullstatic <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7)
E - the Set's element typee1 - the first elemente2 - the second elemente3 - the third elemente4 - the fourth elemente5 - the fifth elemente6 - the sixth elemente7 - the seventh elementSet containing the specified elementsIllegalArgumentException - if there are any duplicate elementsNullPointerException - if an element is nullstatic <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8)
E - the Set's element typee1 - the first elemente2 - the second elemente3 - the third elemente4 - the fourth elemente5 - the fifth elemente6 - the sixth elemente7 - the seventh elemente8 - the eighth elementSet containing the specified elementsIllegalArgumentException - if there are any duplicate elementsNullPointerException - if an element is nullstatic <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9)
E - the Set's element typee1 - the first elemente2 - the second elemente3 - the third elemente4 - the fourth elemente5 - the fifth elemente6 - the sixth elemente7 - the seventh elemente8 - the eighth elemente9 - the ninth elementSet containing the specified elementsIllegalArgumentException - if there are any duplicate elementsNullPointerException - if an element is nullstatic <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10)
E - the Set's element typee1 - the first elemente2 - the second elemente3 - the third elemente4 - the fourth elemente5 - the fifth elemente6 - the sixth elemente7 - the seventh elemente8 - the eighth elemente9 - the ninth elemente10 - the tenth elementSet containing the specified elementsIllegalArgumentException - if there are any duplicate elementsNullPointerException - if an element is null@SafeVarargs static <E> Set<E> of(E... elements)
String[] array = ... ;
Set<String[]> list = Set.<String[]>of(array);
Set.of(E) method
to be invoked instead.E - the Set's element typeelements - the elements to be contained in the setSet containing the specified elementsIllegalArgumentException - if there are any duplicate elementsNullPointerException - if an element is null or if the array is null 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