java.util
Interface Set<E>

All Superinterfaces:
Collection sample code for java.util.Collection definition code for java.util.Collection <E>, Iterable sample code for java.lang.Iterable definition code for java.lang.Iterable <E>
All Known Subinterfaces:
SortedSet sample code for java.util.SortedSet definition code for java.util.SortedSet <E>
All Known Implementing Classes:
AbstractSet sample code for java.util.AbstractSet definition code for java.util.AbstractSet , CopyOnWriteArraySet sample code for java.util.concurrent.CopyOnWriteArraySet definition code for java.util.concurrent.CopyOnWriteArraySet , EnumSet sample code for java.util.EnumSet definition code for java.util.EnumSet , HashSet sample code for java.util.HashSet definition code for java.util.HashSet , JobStateReasons sample code for javax.print.attribute.standard.JobStateReasons definition code for javax.print.attribute.standard.JobStateReasons , LinkedHashSet sample code for java.util.LinkedHashSet definition code for java.util.LinkedHashSet , TreeSet sample code for java.util.TreeSet definition code for java.util.TreeSet

public interface Set<E>
extends Collection sample code for java.util.Collection definition code for java.util.Collection <E>

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.

Since:
1.2
See Also:
Collection sample code for java.util.Collection definition code for java.util.Collection , List sample code for java.util.List definition code for java.util.List , SortedSet sample code for java.util.SortedSet definition code for java.util.SortedSet , HashSet sample code for java.util.HashSet definition code for java.util.HashSet , TreeSet sample code for java.util.TreeSet definition code for java.util.TreeSet , AbstractSet sample code for java.util.AbstractSet definition code for java.util.AbstractSet , Collections.singleton(java.lang.Object) sample code for java.util.Collections.singleton(T) definition code for java.util.Collections.singleton(T) , Collections.EMPTY_SET sample code for java.util.Collections.EMPTY_SET definition code for java.util.Collections.EMPTY_SET

Method Summary
 boolean add sample code for java.util.Set.add(E) definition code for java.util.Set.add(E) (E o)
          Adds the specified element to this set if it is not already present (optional operation).
 boolean addAll sample code for java.util.Set.addAll(java.util.Collection) definition code for java.util.Set.addAll(java.util.Collection) (Collection sample code for java.util.Collection definition code for java.util.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 sample code for java.util.Set.clear() definition code for java.util.Set.clear() ()
          Removes all of the elements from this set (optional operation).
 boolean contains sample code for java.util.Set.contains(java.lang.Object) definition code for java.util.Set.contains(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  o)
          Returns true if this set contains the specified element.
 boolean containsAll sample code for java.util.Set.containsAll(java.util.Collection) definition code for java.util.Set.containsAll(java.util.Collection) (Collection sample code for java.util.Collection definition code for java.util.Collection <?> c)
          Returns true if this set contains all of the elements of the specified collection.
 boolean equals sample code for java.util.Set.equals(java.lang.Object) definition code for java.util.Set.equals(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  o)
          Compares the specified object with this set for equality.
 int hashCode sample code for java.util.Set.hashCode() definition code for java.util.Set.hashCode() ()
          Returns the hash code value for this set.
 boolean isEmpty sample code for java.util.Set.isEmpty() definition code for java.util.Set.isEmpty() ()
          Returns true if this set contains no elements.
 Iterator sample code for java.util.Iterator definition code for java.util.Iterator <E> iterator sample code for java.util.Set.iterator() definition code for java.util.Set.iterator() ()
          Returns an iterator over the elements in this set.
 boolean remove sample code for java.util.Set.remove(java.lang.Object) definition code for java.util.Set.remove(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  o)
          Removes the specified element from this set if it is present (optional operation).
 boolean removeAll sample code for java.util.Set.removeAll(java.util.Collection) definition code for java.util.Set.removeAll(java.util.Collection) (Collection sample code for java.util.Collection definition code for java.util.Collection <?> c)
          Removes from this set all of its elements that are contained in the specified collection (optional operation).
 boolean retainAll sample code for java.util.Set.retainAll(java.util.Collection) definition code for java.util.Set.retainAll(java.util.Collection) (Collection sample code for java.util.Collection definition code for java.util.Collection <?> c)
          Retains only the elements in this set that are contained in the specified collection (optional operation).
 int size sample code for java.util.Set.size() definition code for java.util.Set.size() ()
          Returns the number of elements in this set (its cardinality).
 Object sample code for java.lang.Object definition code for java.lang.Object [] toArray sample code for java.util.Set.toArray() definition code for java.util.Set.toArray() ()
          Returns an array containing all of the elements in this set.
<T> T[]
toArray sample code for java.util.Set.toArray(T[]) definition code for java.util.Set.toArray(T[]) (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.
 

Method Detail

size sample code for java.util.Set.size() definition code for java.util.Set.size()

int size()
Returns the number of elements in this set (its cardinality). If this set contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Specified by:
size sample code for java.util.Collection.size() definition code for java.util.Collection.size() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Returns:
the number of elements in this set (its cardinality).

isEmpty sample code for java.util.Set.isEmpty() definition code for java.util.Set.isEmpty()

boolean isEmpty()
Returns true if this set contains no elements.

Specified by:
isEmpty sample code for java.util.Collection.isEmpty() definition code for java.util.Collection.isEmpty() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Returns:
true if this set contains no elements.

contains sample code for java.util.Set.contains(java.lang.Object) definition code for java.util.Set.contains(java.lang.Object)

boolean contains(Object sample code for java.lang.Object definition code for java.lang.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 sample code for java.util.Collection.contains(java.lang.Object) definition code for java.util.Collection.contains(java.lang.Object) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
o - element whose presence in this set is to be tested.
Returns:
true if this set contains the specified element.
Throws:
ClassCastException sample code for java.lang.ClassCastException definition code for java.lang.ClassCastException - if the type of the specified element is incompatible with this set (optional).
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified element is null and this set does not support null elements (optional).

iterator sample code for java.util.Set.iterator() definition code for java.util.Set.iterator()

Iterator sample code for java.util.Iterator definition code for java.util.Iterator <E> iterator()
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).

Specified by:
iterator sample code for java.util.Collection.iterator() definition code for java.util.Collection.iterator() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Specified by:
iterator sample code for java.lang.Iterable.iterator() definition code for java.lang.Iterable.iterator() in interface Iterable sample code for java.lang.Iterable definition code for java.lang.Iterable <E>
Returns:
an iterator over the elements in this set.

toArray sample code for java.util.Set.toArray() definition code for java.util.Set.toArray()

Object sample code for java.lang.Object definition code for java.lang.Object [] toArray()
Returns an array containing all of the elements in this set. Obeys the general contract of the Collection.toArray method.

Specified by:
toArray sample code for java.util.Collection.toArray() definition code for java.util.Collection.toArray() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Returns:
an array containing all of the elements in this set.

toArray sample code for java.util.Set.<T>toArray(T[]) definition code for java.util.Set.<T>toArray(T[])

<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. Obeys the general contract of the Collection.toArray(Object[]) method.

Specified by:
toArray sample code for java.util.Collection.toArray(T[]) definition code for java.util.Collection.toArray(T[]) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
a - 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.
Returns:
an array containing the elements of this set.
Throws:
ArrayStoreException sample code for java.lang.ArrayStoreException definition code for java.lang.ArrayStoreException - the runtime type of a is not a supertype of the runtime type of every element in this set.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified array is null.

add sample code for java.util.Set.add(E) definition code for java.util.Set.add(E)

boolean add(E o)
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 elements that they may contain.

Specified by:
add sample code for java.util.Collection.add(E) definition code for java.util.Collection.add(E) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
o - element to be added to this set.
Returns:
true if this set did not already contain the specified element.
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the add method is not supported by this set.
ClassCastException sample code for java.lang.ClassCastException definition code for java.lang.ClassCastException - if the class of the specified element prevents it from being added to this set.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified element is null and this set does not support null elements.
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if some aspect of the specified element prevents it from being added to this set.

remove sample code for java.util.Set.remove(java.lang.Object) definition code for java.util.Set.remove(java.lang.Object)

boolean remove(Object sample code for java.lang.Object definition code for java.lang.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 sample code for java.util.Collection.remove(java.lang.Object) definition code for java.util.Collection.remove(java.lang.Object) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
o - object to be removed from this set, if present.
Returns:
true if the set contained the specified element.
Throws:
ClassCastException sample code for java.lang.ClassCastException definition code for java.lang.ClassCastException - if the type of the specified element is incompatible with this set (optional).
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified element is null and this set does not support null elements (optional).
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the remove method is not supported by this set.

containsAll sample code for java.util.Set.containsAll(java.util.Collection<?>) definition code for java.util.Set.containsAll(java.util.Collection<?>)

boolean containsAll(Collection sample code for java.util.Collection definition code for java.util.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 sample code for java.util.Collection.containsAll(java.util.Collection) definition code for java.util.Collection.containsAll(java.util.Collection) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
c - collection to be checked for containment in this set.
Returns:
true if this set contains all of the elements of the specified collection.
Throws:
ClassCastException sample code for java.lang.ClassCastException definition code for java.lang.ClassCastException - if the types of one or more elements in the specified collection are incompatible with this set (optional).
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified collection contains one or more null elements and this set does not support null elements (optional).
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified collection is null.
See Also:
contains(Object) sample code for java.util.Set.contains(java.lang.Object) definition code for java.util.Set.contains(java.lang.Object)

addAll sample code for java.util.Set.addAll(java.util.Collection<? extends E>) definition code for java.util.Set.addAll(java.util.Collection<? extends E>)

boolean addAll(Collection sample code for java.util.Collection definition code for java.util.Collection <? extends E> 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, 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.

Specified by:
addAll sample code for java.util.Collection.addAll(java.util.Collection) definition code for java.util.Collection.addAll(java.util.Collection) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
c - collection whose elements are to be added to this set.
Returns:
true if this set changed as a result of the call.
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the addAll method is not supported by this set.
ClassCastException sample code for java.lang.ClassCastException definition code for java.lang.ClassCastException - if the class of some element of the specified collection prevents it from being added to this set.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified collection contains one or more null elements and this set does not support null elements, or if the specified collection is null.
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if some aspect of some element of the specified collection prevents it from being added to this set.
See Also:
add(Object) sample code for java.util.Set.add(E) definition code for java.util.Set.add(E)

retainAll sample code for java.util.Set.retainAll(java.util.Collection<?>) definition code for java.util.Set.retainAll(java.util.Collection<?>)

boolean retainAll(Collection sample code for java.util.Collection definition code for java.util.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 sample code for java.util.Collection.retainAll(java.util.Collection) definition code for java.util.Collection.retainAll(java.util.Collection) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
c - collection that defines which elements this set will retain.
Returns:
true if this collection changed as a result of the call.
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the retainAll method is not supported by this Collection.
ClassCastException sample code for java.lang.ClassCastException definition code for java.lang.ClassCastException - if the types of one or more elements in this set are incompatible with the specified collection (optional).
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if this set contains a null element and the specified collection does not support null elements (optional).
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified collection is null.
See Also:
remove(Object) sample code for java.util.Set.remove(java.lang.Object) definition code for java.util.Set.remove(java.lang.Object)

removeAll sample code for java.util.Set.removeAll(java.util.Collection<?>) definition code for java.util.Set.removeAll(java.util.Collection<?>)

boolean removeAll(Collection sample code for java.util.Collection definition code for java.util.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 sample code for java.util.Collection.removeAll(java.util.Collection) definition code for java.util.Collection.removeAll(java.util.Collection) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
c - collection that defines which elements will be removed from this set.
Returns:
true if this set changed as a result of the call.
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the removeAll method is not supported by this Collection.
ClassCastException sample code for java.lang.ClassCastException definition code for java.lang.ClassCastException - if the types of one or more elements in this set are incompatible with the specified collection (optional).
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if this set contains a null element and the specified collection does not support null elements (optional).
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified collection is null.
See Also:
remove(Object) sample code for java.util.Set.remove(java.lang.Object) definition code for java.util.Set.remove(java.lang.Object)

clear sample code for java.util.Set.clear() definition code for java.util.Set.clear()

void clear()
Removes all of the elements from this set (optional operation). This set will be empty after this call returns (unless it throws an exception).

Specified by:
clear sample code for java.util.Collection.clear() definition code for java.util.Collection.clear() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the clear method is not supported by this set.

equals sample code for java.util.Set.equals(java.lang.Object) definition code for java.util.Set.equals(java.lang.Object)

boolean equals(Object sample code for java.lang.Object definition code for java.lang.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 sample code for java.util.Collection.equals(java.lang.Object) definition code for java.util.Collection.equals(java.lang.Object) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Overrides:
equals sample code for java.lang.Object.equals(java.lang.Object) definition code for java.lang.Object.equals(java.lang.Object) in class Object sample code for java.lang.Object definition code for java.lang.Object
Parameters:
o - Object to be compared for equality with this set.
Returns:
true if the specified Object is equal to this set.
See Also:
Object.hashCode() sample code for java.lang.Object.hashCode() definition code for java.lang.Object.hashCode() , Hashtable sample code for java.util.Hashtable definition code for java.util.Hashtable

hashCode sample code for java.util.Set.hashCode() definition code for java.util.Set.hashCode()

int hashCode()
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.

Specified by:
hashCode sample code for java.util.Collection.hashCode() definition code for java.util.Collection.hashCode() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Overrides:
hashCode sample code for java.lang.Object.hashCode() definition code for java.lang.Object.hashCode() in class Object sample code for java.lang.Object definition code for java.lang.Object
Returns:
the hash code value for this set.
See Also:
Object.hashCode() sample code for java.lang.Object.hashCode() definition code for java.lang.Object.hashCode() , Object.equals(Object) sample code for java.lang.Object.equals(java.lang.Object) definition code for java.lang.Object.equals(java.lang.Object) , equals(Object) sample code for java.util.Set.equals(java.lang.Object) definition code for java.util.Set.equals(java.lang.Object)