Interface java.util.Set
- All Known Subinterfaces:
- SortedSet
- All Known Implementing Classes:
- AbstractSet, HashSet
- public abstract interface Set
- extends Collection
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 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 Set, 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.
- Since:
- JDK1.2
- See Also:
Collection
,
List
,
SortedSet
,
HashSet
,
TreeSet
,
AbstractSet
,
Collections.singleton(java.lang.Object)
,
Collections.EMPTY_SET
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, whose
runtime type is that of the specified array. |
size
public int size()
- Returns the number of elements in this Set (its cardinality).
- Specified by:
- size in interface Collection
- Returns:
- the number of elements in this Set (its cardinality).
isEmpty
public boolean isEmpty()
- Returns true if this Set contains no elements.
- Specified by:
- isEmpty in interface Collection
- Returns:
- true if this Set contains no elements.
contains
public boolean contains(Object o)
- 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))
.
- Specified by:
- contains in interface Collection
- Returns:
- true if this Set contains the specified element.
iterator
public Iterator iterator()
- Returns an Iterator over the elements in this Set. The elements are
returned in no particular order (unless the Set is an instance of some
class that provides a guarantee).
- Specified by:
- iterator in interface Collection
- Returns:
- an Iterator over the elements in this Set.
toArray
public Object[] toArray()
- Returns an array containing all of the elements in this Set.
Obeys the general contract of Collection.toArray().
- Specified by:
- toArray in interface Collection
- Returns:
- an array containing all of the elements in this Set.
toArray
public Object[] toArray(Object[] a)
- Returns an array containing all of the elements in this Set, whose
runtime type is that of the specified array. Obeys the general
contract of Collection.toArray(Object[]).
- Specified by:
- toArray in interface Collection
- Parameters:
a
- the array into which the elements of the Set are to
be stored, if it is big enough; otherwise, a new array of the
same runtime type is allocated for this purpose.- Returns:
- an array containing the elements of the Set.
- Throws:
- ArrayStoreException - the runtime type of a is not a supertype
of the runtime type of every element in this Set.
add
public boolean add(Object o)
- Adds the specified element to this Set if it is not already present
(optional operation). More formally, adds the specified element,
o
, to the Set if the Set contains no element
e
such that (o==null ? e==null :
o.equals(e))
. If the Set already contains the specified
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.
This stipulation should not be construed to imply that Sets must
accept all elements; Sets have the option of refusing 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.
- Specified by:
- add in interface Collection
- Parameters:
o
- element to be added to this Set.- Returns:
- true if the Set did not already contain the specified element.
- Throws:
- UnsupportedOperationException - add is not supported
by this Set.
- ClassCastException - class of the specified element
prevents it from being added to this Set.
- IllegalArgumentException - some aspect of this element prevents
it from being added to this Set.
remove
public boolean remove(Object o)
- 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.)
- Specified by:
- remove in interface Collection
- Parameters:
o
- object to be removed from this Set, if present.- Returns:
- true if the Set contained the specified element.
- Throws:
- UnsupportedOperationException - remove is not supported
by this Set.
containsAll
public boolean containsAll(Collection c)
- 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.
- Specified by:
- containsAll in interface Collection
- Returns:
- true if this Set contains all of the elements of the
specified Collection.
addAll
public boolean addAll(Collection c)
- 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, this 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.
- Specified by:
- addAll in interface Collection
- Returns:
- true if this Set changed as a result of the call.
- Throws:
- UnsupportedOperationException - addAll is not supported
by this Set.
- ClassCastException - class of some element of the specified
Collection prevents it from being added to this Set.
- IllegalArgumentException - some aspect of some element of the
specified Collection prevents it from being added to this
Set.
- See Also:
add(Object)
retainAll
public boolean retainAll(Collection c)
- 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.
- Specified by:
- retainAll in interface Collection
- Returns:
- true if this Collection changed as a result of the call.
- Throws:
- UnsupportedOperationException - retainAll is not supported
by this Collection.
- See Also:
remove(Object)
removeAll
public boolean removeAll(Collection c)
- 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.
- Specified by:
- removeAll in interface Collection
- Returns:
- true if this Set changed as a result of the call.
- Throws:
- UnsupportedOperationException - removeAll is not supported
by this Collection.
- See Also:
remove(Object)
clear
public void clear()
- Removes all of the elements from this Set (optional operation). The
Set will be empty after this call returns (unless it throws an
exception).
- Specified by:
- clear in interface Collection
- Throws:
- UnsupportedOperationException - clear is not supported
by this Set.
equals
public boolean equals(Object o)
- 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.
- Specified by:
- equals in interface Collection
- Parameters:
o
- Object to be compared for equality with this Set.- Returns:
- true if the specified Object is equal to this Set.
- Overrides:
- equals in class Object
hashCode
public int hashCode()
- Returns the hash code value for this Set. The hash code of a Set is
defined to be the sum of the hashCodes 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 Object.hashCode.
- Specified by:
- hashCode in interface Collection
- Returns:
- the hash code value for this Set.
- Overrides:
- hashCode in class Object
- See Also:
Object.hashCode()
,
Object.equals(Object)
,
equals(Object)
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