AbstractSet

public abstract class AbstractSet extends AbstractCollection<E>
implements Set<E>

Known Direct Subclasses ConcurrentSkipListSet<E>, CopyOnWriteArraySet<E>, EnumSet<E extends Enum<E>>, HashSet<E>, TreeSet<E> ConcurrentSkipListSet<E> A scalable concurrent NavigableSet implementation based on a ConcurrentSkipListMap.  CopyOnWriteArraySet<E> A Set that uses an internal CopyOnWriteArrayList for all of its operations.  EnumSet<E extends Enum<E>> A specialized Set implementation for use with enum types.  HashSet<E> This class implements the Set interface, backed by a hash table (actually a HashMap instance).  TreeSet<E> A NavigableSet implementation based on a TreeMap.

Known Indirect Subclasses LinkedHashSet<E> LinkedHashSet<E> Hash table and linked list implementation of the Set interface, with predictable iteration order.

This class provides a skeletal implementation of the Set interface to minimize the effort required to implement this interface.

The process of implementing a set by extending this class is identical to that of implementing a Collection by extending AbstractCollection, except that all of the methods and constructors in subclasses of this class must obey the additional constraints imposed by the Set interface (for instance, the add method must not permit addition of multiple instances of an object to a set).

Note that this class does not override any of the implementations from the AbstractCollection class. It merely adds implementations for equals and hashCode.

This class is a member of the Java Collections Framework.

See Also

• Collection
• AbstractCollection
• Set

Protected Constructor Summary

AbstractSet() Sole constructor.

Public Method Summary

boolean	equals(Object o) Compares the specified object with this set for equality.
int	hashCode() Returns the hash code value for this set.
boolean	removeAll(Collection<?> c) Removes from this set all of its elements that are contained in the specified collection (optional operation).

Inherited Method Summary

From class java.util.AbstractCollection

boolean	add(E e) Ensures that this collection contains the specified element (optional operation). This implementation always throws an UnsupportedOperationException.
boolean	addAll(Collection<? extends E> c) Adds all of the elements in the specified collection to this collection (optional operation). This implementation iterates over the specified collection, and adds each object returned by the iterator to this collection, in turn.
void	clear() Removes all of the elements from this collection (optional operation). This implementation iterates over this collection, removing each element using the Iterator.remove operation.
boolean	contains(Object o) Returns true if this collection contains the specified element. This implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element.
boolean	containsAll(Collection<?> c) Returns true if this collection contains all of the elements in the specified collection. This implementation iterates over the specified collection, checking each element returned by the iterator in turn to see if it's contained in this collection.
boolean	isEmpty() Returns true if this collection contains no elements. This implementation returns size() == 0.
abstract Iterator<E>	iterator() Returns an iterator over the elements contained in this collection.
boolean	remove(Object o) Removes a single instance of the specified element from this collection, if it is present (optional operation). This implementation iterates over the collection looking for the specified element.
boolean	removeAll(Collection<?> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation). This implementation iterates over this collection, checking each element returned by the iterator in turn to see if it's contained in the specified collection.
boolean	retainAll(Collection<?> c) Retains only the elements in this collection that are contained in the specified collection (optional operation). This implementation iterates over this collection, checking each element returned by the iterator in turn to see if it's contained in the specified collection.
abstract int	size() Returns the number of elements in this collection.
<T> T[]	toArray(T[] contents) Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. This implementation returns an array containing all the elements returned by this collection's iterator in the same order, stored in consecutive elements of the array, starting with index 0.
Object[]	toArray() Returns an array containing all of the elements in this collection. This implementation returns an array containing all the elements returned by this collection's iterator, in the same order, stored in consecutive elements of the array, starting with index 0.
String	toString() Returns a string representation of this collection.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

From interface java.util.Collection

abstract boolean	add(E e) Ensures that this collection contains the specified element (optional operation).
abstract boolean	addAll(Collection<? extends E> c) Adds all of the elements in the specified collection to this collection (optional operation).
abstract void	clear() Removes all of the elements from this collection (optional operation).
abstract boolean	contains(Object o) Returns true if this collection contains the specified element.
abstract boolean	containsAll(Collection<?> c) Returns true if this collection contains all of the elements in the specified collection.
abstract boolean	equals(Object o) Compares the specified object with this collection for equality.
abstract int	hashCode() Returns the hash code value for this collection.
abstract boolean	isEmpty() Returns true if this collection contains no elements.
abstract Iterator<E>	iterator() Returns an iterator over the elements in this collection.
Stream<E>	parallelStream() Returns a possibly parallel Stream with this collection as its source.
abstract boolean	remove(Object o) Removes a single instance of the specified element from this collection, if it is present (optional operation).
abstract boolean	removeAll(Collection<?> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation).
boolean	removeIf(Predicate<? super E> filter) Removes all of the elements of this collection that satisfy the given predicate.
abstract boolean	retainAll(Collection<?> c) Retains only the elements in this collection that are contained in the specified collection (optional operation).
abstract int	size() Returns the number of elements in this collection.
Spliterator<E>	spliterator() Creates a Spliterator over the elements in this collection.
Stream<E>	stream() Returns a sequential Stream with this collection as its source.
abstract <T> T[]	toArray(T[] a) Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
abstract Object[]	toArray() Returns an array containing all of the elements in this collection.

From interface java.util.Set

abstract boolean	add(E e) Adds the specified element to this set if it is not already present (optional operation).
abstract boolean	addAll(Collection<? extends E> c) Adds all of the elements in the specified collection to this set if they're not already present (optional operation).
abstract void	clear() Removes all of the elements from this set (optional operation).
abstract boolean	contains(Object o) Returns true if this set contains the specified element.
abstract boolean	containsAll(Collection<?> c) Returns true if this set contains all of the elements of the specified collection.
abstract boolean	equals(Object o) Compares the specified object with this set for equality.
abstract int	hashCode() Returns the hash code value for this set.
abstract boolean	isEmpty() Returns true if this set contains no elements.
abstract Iterator<E>	iterator() Returns an iterator over the elements in this set.
abstract boolean	remove(Object o) Removes the specified element from this set if it is present (optional operation).
abstract boolean	removeAll(Collection<?> c) Removes from this set all of its elements that are contained in the specified collection (optional operation).
abstract boolean	retainAll(Collection<?> c) Retains only the elements in this set that are contained in the specified collection (optional operation).
abstract int	size() Returns the number of elements in this set (its cardinality).
Spliterator<E>	spliterator() Creates a Spliterator over the elements in this set.
abstract <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.
abstract Object[]	toArray() Returns an array containing all of the elements in this set.

From interface java.lang.Iterable

void	forEach(Consumer<? super T> action) Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.
abstract Iterator<E>	iterator() Returns an iterator over elements of type T.
Spliterator<E>	spliterator() Creates a Spliterator over the elements described by this Iterable.

Protected Constructors

protected AbstractSet ()

Sole constructor. (For invocation by subclass constructors, typically implicit.)

Public Methods

public 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.

This implementation first checks if the specified object is this set; if so it returns true. Then, it checks if the specified object is a set whose size is identical to the size of this set; if not, it returns false. If so, it returns containsAll((Collection) o).

Parameters

o	object to be compared for equality with this set

Returns

• true if the specified object is equal to this set

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 hash codes of the elements in the set, where the hash code 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().

This implementation iterates over the set, calling the hashCode method on each element in the set, and adding up the results.

Returns

• the hash code value for this set

See Also

• Object.equals(Object)
• Set.equals(Object)

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.

This implementation determines which is the smaller of this set and the specified collection, by invoking the size method on each. If this set has fewer elements, then the implementation iterates over this set, checking each element returned by the iterator in turn to see if it is contained in the specified collection. If it is so contained, it is removed from this set with the iterator's remove method. If the specified collection has fewer elements, then the implementation iterates over the specified collection, removing from this set each element returned by the iterator, using this set's remove method.

Note that this implementation will throw an UnsupportedOperationException if the iterator returned by the iterator method does not implement the remove method.

Parameters

c	collection containing elements to be removed from this set

Returns

• true if this set changed as a result of the call

Throws

UnsupportedOperationException	if the removeAll operation is not supported by this set
ClassCastException	if the class of an element of this set is incompatible with the specified collection (optional)
NullPointerException	if this set contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null

See Also

• AbstractCollection.remove(Object)
• AbstractCollection.contains(Object)