| java.util.Set
All known Subclasses: java.util.LinkedHashSet, java.util.HashSet, java.util.AbstractSet,
| Set | | public interface Set extends Collection(Code) | | A collection that contains no duplicate elements. More formally, sets
contain no pair of elements 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.
This interface is a member of the
Java Collections Framework.
author:
Josh Bloch
version:
1.23, 02/02/00
See Also: Collection
See Also: List
See Also: SortedSet
See Also: HashSet
See Also: TreeSet
See Also: AbstractSet
See Also: Collections.singleton(java.lang.Object)
See Also: Collections.EMPTY_SET
since:
1.2 |
| Method Summary | |
| boolean | add(Object o)
Adds the specified element to this set if it is not already present
(optional operation). | | boolean | addAll(Collection 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 | 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 (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). | | Object[] | toArray()
Returns an array containing all of the elements in this set. | | Object[] | toArray(Object 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. |
| add | | boolean add(Object o)(Code) | | Adds the specified element to this set if it is not already present
(optional operation). More formally, adds the specified element,
o, to this set if this set contains no element
e such that (o==null ? e==null :
o.equals(e)). If this set already contains the specified
element, the call leaves this 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 throwing an exception, as described in the
specification for Collection.add. Individual set
implementations should clearly document any restrictions on the the
elements that they may contain.
Parameters:
o - element to be added to this set. true if this set did not already contain the specifiedelement.
throws:
UnsupportedOperationException - if the add method is notsupported by this set.
throws:
ClassCastException - if the class of the specified elementprevents it from being added to this set.
throws:
NullPointerException - if the specified element is null and thisset does not support null elements.
throws:
IllegalArgumentException - if some aspect of the specified elementprevents it from being added to this set. |
| addAll | | boolean addAll(Collection c)(Code) | | Adds all of the elements in the specified collection to this set if
they're not already present (optional operation). If the specified
collection is also a set, the addAll operation effectively
modifies this set so that its value is the union of the two
sets. The behavior of this operation is unspecified if the specified
collection is modified while the operation is in progress.
Parameters:
c - collection whose elements are to be added to this set. true if this set changed as a result of the call.
throws:
UnsupportedOperationException - if the addAll method isnot supported by this set.
throws:
ClassCastException - if the class of some element of thespecified collection prevents it from being added to thisset.
throws:
NullPointerException - if the specified collection contains oneor more null elements and this set does not support nullelements, or if the specified collection is null.
throws:
IllegalArgumentException - if some aspect of some element of thespecified collection prevents it from being added to thisset.
See Also: Set.add(Object) |
| clear | | void clear()(Code) | | Removes all of the elements from this set (optional operation).
This set will be empty after this call returns (unless it throws an
exception).
throws:
UnsupportedOperationException - if the clear methodis not supported by this set. |
| contains | | boolean contains(Object o)(Code) | | Returns true if this set contains the specified element. More
formally, returns true if and only if this set contains an
element e such that (o==null ? e==null :
o.equals(e)).
Parameters:
o - element whose presence in this set is to be tested. true if this set contains the specified element.
throws:
ClassCastException - if the type of the specified elementis incompatible with this set (optional).
throws:
NullPointerException - if the specified element is null and thisset does not support null elements (optional). |
| containsAll | | boolean containsAll(Collection c)(Code) | | Returns 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.
Parameters:
c - collection to be checked for containment in this set. true if this set contains all of the elements of thespecified collection.
throws:
ClassCastException - if the types of one or more elementsin the specified collection are incompatible with thisset (optional).
throws:
NullPointerException - if the specified collection contains oneor more null elements and this set does not support nullelements (optional).
throws:
NullPointerException - if the specified collection isnull.
See Also: Set.contains(Object) |
| equals | | boolean equals(Object o)(Code) | | Compares the specified object with this set for equality. Returns
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.
Parameters:
o - Object to be compared for equality with this set. true if the specified Object is equal to this set. |
| hashCode | | int hashCode()(Code) | | Returns the hash code value for this set. The hash code of a set is
defined to be the sum of the hash codes of the elements in the set,
where the hashcode of a 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 the Object.hashCode method.
the hash code value for this set.
See Also: Object.hashCode
See Also: Object.equals(Object)
See Also: Set.equals(Object) |
| isEmpty | | boolean isEmpty()(Code) | | Returns true if this set contains no elements.
true if this set contains no elements. |
| iterator | | Iterator iterator()(Code) | | Returns an iterator over the elements in this set. The elements are
returned in no particular order (unless this set is an instance of some
class that provides a guarantee).
an iterator over the elements in this set. |
| remove | | boolean remove(Object o)(Code) | | Removes the specified element from this set if it is present (optional
operation). More formally, removes an element e such that
(o==null ? e==null : o.equals(e)), if the set contains
such an element. Returns true if the set contained the
specified element (or equivalently, if the set changed as a result of
the call). (The set will not contain the specified element once the
call returns.)
Parameters:
o - object to be removed from this set, if present. true if the set contained the specified element.
throws:
ClassCastException - if the type of the specified elementis incompatible with this set (optional).
throws:
NullPointerException - if the specified element is null and thisset does not support null elements (optional).
throws:
UnsupportedOperationException - if the remove method isnot supported by this set. |
| removeAll | | boolean removeAll(Collection c)(Code) | | Removes from this set all of its elements that are contained in the
specified collection (optional operation). If the specified
collection is also a set, this operation effectively modifies this
set so that its value is the asymmetric set difference of
the two sets.
Parameters:
c - collection that defines which elements will be removed fromthis set. true if this set changed as a result of the call.
throws:
UnsupportedOperationException - if the removeAllmethod is not supported by this Collection.
throws:
ClassCastException - if the types of one or more elements in thisset are incompatible with the specified collection(optional).
throws:
NullPointerException - if this set contains a null element andthe specified collection does not support null elements(optional).
throws:
NullPointerException - if the specified collection isnull.
See Also: Set.remove(Object) |
| retainAll | | boolean retainAll(Collection c)(Code) | | Retains only the elements in this set that are contained in the
specified collection (optional operation). In other words, removes
from this set all of its elements that are not contained in the
specified collection. If the specified collection is also a set, this
operation effectively modifies this set so that its value is the
intersection of the two sets.
Parameters:
c - collection that defines which elements this set will retain. true if this collection changed as a result of thecall.
throws:
UnsupportedOperationException - if the retainAll methodis not supported by this Collection.
throws:
ClassCastException - if the types of one or more elements in thisset are incompatible with the specified collection(optional).
throws:
NullPointerException - if this set contains a null element andthe specified collection does not support null elements(optional).
throws:
NullPointerException - if the specified collection isnull.
See Also: Set.remove(Object) |
| size | | int size()(Code) | | Returns the number of elements in this set (its cardinality). If this
set contains more than Integer.MAX_VALUE elements, returns
Integer.MAX_VALUE.
the number of elements in this set (its cardinality). |
| toArray | | Object[] toArray()(Code) | | Returns an array containing all of the elements in this set.
Obeys the general contract of the Collection.toArray method.
an array containing all of the elements in this set. |
| toArray | | Object[] toArray(Object a)(Code) | | Returns an array containing all of the elements in this set; the
runtime type of the returned array is that of the specified array.
Obeys the general contract of the
Collection.toArray(Object[]) method.
Parameters:
a - the array into which the elements of this set are tobe stored, if it is big enough; otherwise, a new array of thesame runtime type is allocated for this purpose. an array containing the elements of this set.
throws:
ArrayStoreException - the runtime type of a is not a supertypeof the runtime type of every element in this set.
throws:
NullPointerException - if the specified array is null. |
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