AbstractSet

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

java.lang.Object
   ↳ java.util.AbstractCollection<E>
     ↳ java.util.AbstractSet<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
LinkedHashSet<E>

Hash table and linked list implementation of the Set interface, with well-defined encounter 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.

Summary

Protected constructors

AbstractSet()

Sole constructor.

Public methods

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 methods

boolean add(E e)

Ensures that this collection contains the specified element (optional operation).

boolean addAll(Collection<? extends E> c)

Adds all of the elements in the specified collection to this collection (optional operation).

void clear()

Removes all of the elements from this collection (optional operation).

boolean contains(Object o)

Returns true if this collection contains the specified element.

boolean containsAll(Collection<?> c)

Returns true if this collection contains all of the elements in the specified collection.

boolean isEmpty()

Returns true if this collection contains no elements.

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).

boolean removeAll(Collection<?> c)

Removes all of this collection's elements that are also contained in the specified collection (optional operation).

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.

<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.

Object[] toArray()

Returns an array containing all of the elements in this collection.

String toString()

Returns a string representation of this collection.

Object clone()

Creates and returns a copy of this object.

boolean equals(Object obj)

Indicates whether some other object is "equal to" this one.

void finalize()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

final Class<?> getClass()

Returns the runtime class of this Object.

int hashCode()

Returns a hash code value for the object.

final void notify()

Wakes up a single thread that is waiting on this object's monitor.

final void notifyAll()

Wakes up all threads that are waiting on this object's monitor.

String toString()

Returns a string representation of the object.

final void wait(long timeoutMillis, int nanos)

Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

final void wait(long timeoutMillis)

Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

final void wait()

Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

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.

default 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).

default 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.

default Spliterator<E> spliterator()

Creates a Spliterator over the elements in this collection.

default 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.

default <T> T[] toArray(IntFunction<T[]> generator)

Returns an array containing all of the elements in this collection, using the provided generator function to allocate the returned array.

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.

static <E> Set<E> copyOf(Collection<? extends E> coll)

Returns an unmodifiable Set containing the elements of the given 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.

static <E> Set<E> of(E e1, E e2, E e3)

Returns an unmodifiable set containing three elements.

static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9)

Returns an unmodifiable set containing nine elements.

static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5)

Returns an unmodifiable set containing five elements.

static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6)

Returns an unmodifiable set containing six elements.

static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8)

Returns an unmodifiable set containing eight elements.

static <E> Set<E> of(E... elements)

Returns an unmodifiable set containing an arbitrary number of elements.

static <E> Set<E> of()

Returns an unmodifiable set containing zero elements.

static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10)

Returns an unmodifiable set containing ten elements.

static <E> Set<E> of(E e1, E e2)

Returns an unmodifiable set containing two elements.

static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7)

Returns an unmodifiable set containing seven elements.

static <E> Set<E> of(E e1, E e2, E e3, E e4)

Returns an unmodifiable set containing four elements.

static <E> Set<E> of(E e1)

Returns an unmodifiable set containing one element.

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).

default Spliterator<E> spliterator()

Creates a Spliterator over the elements in this set.

abstract Object[] toArray()

Returns an array containing all of 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.

default 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.

default Spliterator<E> spliterator()

Creates a Spliterator over the elements described by this Iterable.

Protected constructors

AbstractSet

Added in API level 1
protected AbstractSet ()

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

Public methods

equals

Added in API level 1
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: object to be compared for equality with this set

Returns
boolean true if the specified object is equal to this set

hashCode

Added in API level 1
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
int the hash code value for this set

removeAll

Added in API level 1
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: collection containing elements to be removed from this set

Returns
boolean 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