oracle.jbo.server.java.util
Interface Set

All Superinterfaces:

Collection

All Known Implementing Classes:

AbstractSet, ArraySet

public 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 contain no duplicate elements (as defined above).

Implemented by HashSet, ArraySet.

Since:

JDK1.2

See Also:

Collection, List, HashSet, ArraySet, AbstractSet

Method Summary

boolean	add(java.lang.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(java.lang.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(java.lang.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(java.lang.Object o) Removes the given 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).
java.lang.Object[]	toArray() Returns an array containing all of the elements in this Set.

Method Detail

size

public int size()

Returns the number of elements in this Set (its cardinality).

Specified by:

size in interface Collection

Since:

JDK1.2

isEmpty

public boolean isEmpty()

Returns true if this Set contains no elements.

Specified by:

isEmpty in interface Collection

Since:

JDK1.2

contains

public boolean contains(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 in interface Collection

Parameters:

o - element whose presence in this Collection is to be tested.

Since:

JDK1.2

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

Since:

JDK1.2

toArray

public java.lang.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

Since:

JDK1.2

add

public boolean add(java.lang.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.

java.lang.ClassCastException - class of the specified element prevents it from being added to this Set.

java.lang.IllegalArgumentException - some aspect of this element prevents it from being added to this Set.

Since:

JDK1.2

remove

public boolean remove(java.lang.Object o)

Removes the given 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.

Since:

JDK1.2

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

Since:

JDK1.2

See Also:

Collection.contains(Object)

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

Parameters:

c - elements to be inserted into this Collection.

Returns:

true if this Set changed as a result of the call.

Throws:

UnsupportedOperationException - addAll is not supported by this Set.

java.lang.ClassCastException - class of some element of the specified Collection prevents it from being added to this Set.

java.lang.IllegalArgumentException - some aspect of some element of the specified Collection prevents it from being added to this Set.

Since:

JDK1.2

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

Parameters:

c - elements to be retained in this Collection.

Returns:

true if this Collection changed as a result of the call.

Throws:

UnsupportedOperationException - retainAll is not supported by this Collection.

Since:

JDK1.2

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

Parameters:

c - elements to be removed from this Collection.

Returns:

true if this Set changed as a result of the call.

Throws:

UnsupportedOperationException - removeAll is not supported by this Collection.

Since:

JDK1.2

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.

Since:

JDK1.2

equals

public boolean equals(java.lang.Object o)

Compares the specified Object with this Set for equality. Returns true if the given object is also a Set, the two Sets have the same size, and every member of the given Set is contained in this Set. This 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.

Since:

JDK1.2

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

Since:

JDK1.2

See Also:

Object.hashCode(), Object.equals(Object), equals(Object)