Class AbstractSet<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractSet<E>

Type Parameters:

E - the type of elements maintained by this set

All Implemented Interfaces:

Iterable<E>, Collection<E>, Set<E>

Direct Known Subclasses:

ConcurrentSkipListSet, CopyOnWriteArraySet, EnumSet, HashSet, TreeSet

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

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.

Since:

1.2

See Also:

• Collection
• AbstractCollection
• Set

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	AbstractSet()	Sole constructor.

Method Summary

Modifier and Type	Method	Description
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).

Methods declared in class AbstractCollection

add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, retainAll, toArray, toArray, toString

Modifier and Type	Method	Description
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	retainAll(Collection<?> c)	Retains only the elements in this collection that are contained in the specified collection (optional operation).
Object[]	toArray()	Returns an array containing all of the 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.
String	toString()	Returns a string representation of this collection.

Methods declared in class Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Modifier and Type	Method	Description
protected Object	clone()	Creates and returns a copy of this object.
protected void	finalize()	Deprecated, for removal: This API element is subject to removal in a future version. Finalization is deprecated and subject to removal in a future release.
final Class<?>	getClass()	Returns the runtime class of this 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.
final void	wait()	Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
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(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.

Methods declared in interface Collection

parallelStream, removeIf, stream, toArray

Modifier and Type	Method	Description
default Stream<E>	parallelStream()	Returns a possibly parallel Stream with this collection as its source.
default boolean	removeIf(Predicate<? super E> filter)	Removes all of the elements of this collection that satisfy the given predicate (optional operation).
default Stream<E>	stream()	Returns a sequential Stream with this collection as its source.
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.

Methods declared in interface Iterable

forEach

Modifier and Type	Method	Description
default void	forEach(Consumer<? super E> action)	Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.

Methods declared in interface Set

add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, retainAll, size, spliterator, toArray, toArray

Modifier and Type	Method	Description
boolean	add(E e)	Adds the specified element to this set if it is not already present (optional operation).
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).
void	clear()	Removes all of the elements from this set (optional operation).
boolean	contains(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	isEmpty()	Returns true if this set contains no elements.
Iterator<E>	iterator()	Returns an iterator over the elements in this set.
boolean	remove(Object o)	Removes the specified element from this set if it is present (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).
default Spliterator<E>	spliterator()	Creates a Spliterator over the elements in this set.
Object[]	toArray()	Returns an array containing all of the elements in this set.
<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.

Constructor Details

AbstractSet

protected AbstractSet()

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

Method Details

equals

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).

Specified by:

equals in interface Collection<E>

Specified by:

equals in interface Set<E>

Overrides:

equals in class 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.equals(Object)
• Set.equals(Object)
• List.equals(Object)

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 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.

Specified by:

hashCode in interface Collection<E>

Specified by:

hashCode in interface Set<E>

Overrides:

hashCode in class Object

Returns:

the hash code value for this set

See Also:

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

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.

Specified by:

removeAll in interface Collection<E>

Specified by:

removeAll in interface Set<E>

Overrides:

removeAll in class AbstractCollection<E>

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)