public interface java.util.Set<A>

java.lang.Object
   |
   +----java.util.Set<A>

public interface Set<A>
  implements Collection<A>

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.

See also:

Collection, List, HashSet, ArraySet, AbstractSet

add(A)

Adds the specified element to this Set if it is not already present (optional operation)

addAll(Collection<A>)

Adds all of the elements in the specified Collection to this Set if they're not already

clear()

Removes all of the elements from this Set (optional operation)

contains(A)

Returns true if this Set contains the specified element

containsAll(Collection<A>)

Returns true if this Set contains all of the elements of the specified Collection

equals(Object)

Compares the specified Object with this Set for equality. Returns true if the given

hashCode()

Returns the hash code value for this Set

isEmpty()

Returns true if this Set contains no elements.

iterator()

Returns an Iterator over the elements in this Set

remove(A)

Removes the given element from this Set if it is present (optional operation)

removeAll(Collection<A>)

Removes from this Set all of its elements that are contained in the specified Collection

retainAll(Collection<A>)

Retains only the elements in this Set that are contained in the specified Collection

size()

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

toArray()

Returns an array containing all of the elements in this Set. Obeys the general contract

public abstract int size();

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

isEmpty

public abstract boolean isEmpty();

Returns true if this Set contains no elements.

contains

public abstract boolean contains(A 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)).

iterator

public abstract Iterator<A> 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).

toArray

public abstract Object[] toArray();

Returns an array containing all of the elements in this Set. Obeys the general contract of Collection.toArray.

add

public abstract boolean add(A 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.

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 abstract boolean remove(A 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.)

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 abstract boolean containsAll(Collection<A> 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.

addAll

public abstract boolean addAll(Collection<A> 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.

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 abstract boolean retainAll(Collection<A> 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.

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 abstract boolean removeAll(Collection<A> 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.

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 abstract 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).

Throws:

UnsupportedOperationException -clear is not supported by this Set.

equals

public abstract boolean equals(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.

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 abstract 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.

Overrides:

hashCode in class Object

See also:

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

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