Class ConcurrentHashMap.KeySetView<K,V>

java.lang.Object

java.util.AbstractCollection<K>

java.util.AbstractSet<K>

java.util.concurrent.ConcurrentHashMap.KeySetView<K,V>

All Implemented Interfaces:

Serializable, Iterable<K>, Collection<K>, Set<K>

Enclosing class:

ConcurrentHashMap<K,V>

public static class ConcurrentHashMap.KeySetView<K,V>
extends AbstractSet<K>
implements Serializable

java.util.concurrent.ConcurrentHashMap.KeySetView: the keys of a map as a set. A view created with a mapped value (keySet(V), newKeySet()) also accepts add, which maps the key to that value.

See Also:

• Serialized Form

Method Summary

Modifier and Type	Method	Description
boolean	add(K e)	Attempts to add object to the contents of this Collection (optional).
boolean	addAll(Collection<? extends K> c)	Attempts to add all of the objects contained in collection to the contents of this Collection (optional).
void	clear()	Removes all elements from this Collection, leaving it empty (optional).
boolean	contains(Object o)	Tests whether this Collection contains the specified object.
ConcurrentHashMap<K,V>	getMap()	The map this is a view of.
V	getMappedValue()
boolean	isEmpty()	Returns if this Collection contains no elements.
Iterator<K>	iterator()	Returns an instance of Iterator that may be used to access the objects contained by this Collection.
boolean	remove(Object o)	Removes one instance of the specified object from this Collection if one is contained (optional).
int	size()	Returns a count of how many objects this Collection contains.

Methods inherited from class AbstractSet

equals, hashCode, removeAll

Methods inherited from class AbstractCollection

containsAll, retainAll, toArray, toArray, toString

Methods inherited from class Object

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

Methods inherited from interface Collection

parallelStream, removeIf, stream, toArray

Methods inherited from interface Iterable

forEach

Methods inherited from interface Set

containsAll, retainAll, spliterator, toArray, toArray

Method Details

getMap

public ConcurrentHashMap<K,V> getMap()

The map this is a view of. It is the live map, as in the JDK: the view exists to share it.

getMappedValue

public V getMappedValue()

iterator

public Iterator<K> iterator()

Description copied from class: AbstractCollection

Returns an instance of Iterator that may be used to access the objects contained by this Collection. The order in which the elements are returned by the Iterator is not defined unless the instance of the Collection has a defined order. In that case, the elements are returned in that order.

In this class this method is declared abstract and has to be implemented by concrete Collection implementations.

Returns

an iterator for accessing the Collection contents.

Specified by:

iterator in interface Collection<K>

Specified by:

iterator in interface Iterable<K>

Specified by:

iterator in interface Set<K>

Specified by:

iterator in class AbstractCollection<K>

size

public int size()

Description copied from class: AbstractCollection

Returns a count of how many objects this Collection contains.

In this class this method is declared abstract and has to be implemented by concrete Collection implementations.

Returns

Specified by:

size in interface Collection<K>

Specified by:

size in interface Set<K>

Specified by:

size in class AbstractCollection<K>

Returns:

how many objects this Collection contains, or Integer.MAX_VALUE if there are more than Integer.MAX_VALUE elements in this Collection.

isEmpty

public boolean isEmpty()

Description copied from class: AbstractCollection

Returns if this Collection contains no elements. This implementation tests, whether size returns 0.

Returns

Specified by:

isEmpty in interface Collection<K>

Specified by:

isEmpty in interface Set<K>

Overrides:

isEmpty in class AbstractCollection<K>

Returns:

true if this Collection has no elements, false otherwise.

See also

• #size

contains

public boolean contains(Object o)

Description copied from class: AbstractCollection

Tests whether this Collection contains the specified object. This implementation iterates over this Collection and tests, whether any element is equal to the given object. If object != null then object.equals(e) is called for each element e returned by the iterator until the element is found. If object == null then each element e returned by the iterator is compared with the test e == null.

Parameters

• object: the object to search for.

Returns

true if object is an element of this Collection, false otherwise.

Throws

• ClassCastException: if the object to look for isn't of the correct type.

• NullPointerException: @throws NullPointerException if the object to look for is null and this Collection doesn't support null elements.

Specified by:

contains in interface Collection<K>

Specified by:

contains in interface Set<K>

Overrides:

contains in class AbstractCollection<K>

Returns:

true if object is an element of this Collection, false otherwise.

Throws

• ClassCastException: @throws ClassCastException if the object to look for isn't of the correct type.

• NullPointerException: @throws NullPointerException if the object to look for is null and this Collection doesn't support null elements.

remove

public boolean remove(Object o)

Description copied from class: AbstractCollection

Removes one instance of the specified object from this Collection if one is contained (optional). This implementation iterates over this Collection and tests for each element e returned by the iterator, whether e is equal to the given object. If object != null then this test is performed using object.equals(e), otherwise using object == null. If an element equal to the given object is found, then the remove method is called on the iterator and true is returned, false otherwise. If the iterator does not support removing elements, an UnsupportedOperationException is thrown.

Parameters

• object: the object to remove.

Returns

Specified by:

remove in interface Collection<K>

Specified by:

remove in interface Set<K>

Overrides:

remove in class AbstractCollection<K>

Returns:

true if this Collection is modified, false otherwise.

Throws

• UnsupportedOperationException: if removing from this Collection is not supported.

• ClassCastException: if the object passed is not of the correct type.

• NullPointerException: @throws NullPointerException if object is null and this Collection doesn't support null elements.

clear

public void clear()

Description copied from class: AbstractCollection

Removes all elements from this Collection, leaving it empty (optional). This implementation iterates over this Collection and calls the remove method on each element. If the iterator does not support removal of elements, an UnsupportedOperationException is thrown.

Concrete implementations usually can clear a Collection more efficiently and should therefore overwrite this method.

Throws

• UnsupportedOperationException: @throws UnsupportedOperationException it the iterator does not support removing elements from this Collection

See also

• #iterator

• #isEmpty

• #size

Specified by:

clear in interface Collection<K>

Specified by:

clear in interface Set<K>

Overrides:

clear in class AbstractCollection<K>

add

public boolean add(K e)

Description copied from interface: Collection

Attempts to add object to the contents of this Collection (optional).

After this method finishes successfully it is guaranteed that the object is contained in the collection.

If the collection was modified it returns true, false if no changes were made.

An implementation of Collection may narrow the set of accepted objects, but it has to specify this in the documentation. If the object to be added does not meet this restriction, then an IllegalArgumentException is thrown.

If a collection does not yet contain an object that is to be added and adding the object fails, this method must throw an appropriate unchecked Exception. Returning false is not permitted in this case because it would violate the postcondition that the element will be part of the collection after this method finishes.

Parameters

• object: the object to add.

Returns

Specified by:

add in interface Collection<K>

Specified by:

add in interface Set<K>

Overrides:

add in class AbstractCollection<K>

Returns:

true if this Collection is modified, false otherwise.

Throws

• UnsupportedOperationException: if adding to this Collection is not supported.

• ClassCastException: @throws ClassCastException if the class of the object is inappropriate for this collection.

• IllegalArgumentException: if the object cannot be added to this Collection.

• NullPointerException: if null elements cannot be added to the Collection.

addAll

public boolean addAll(Collection<? extends K> c)

Description copied from class: AbstractCollection

Attempts to add all of the objects contained in collection to the contents of this Collection (optional). This implementation iterates over the given Collection and calls add for each element. If any of these calls return true, then true is returned as result of this method call, false otherwise. If this Collection does not support adding elements, an UnsupportedOperationException is thrown.

If the passed Collection is changed during the process of adding elements to this Collection, the behavior depends on the behavior of the passed Collection.

Parameters

• collection: the collection of objects.

Returns

Specified by:

addAll in interface Collection<K>

Specified by:

addAll in interface Set<K>

Overrides:

addAll in class AbstractCollection<K>

Returns:

true if this Collection is modified, false otherwise.

Throws

• UnsupportedOperationException: if adding to this Collection is not supported.

• ClassCastException: @throws ClassCastException if the class of an object is inappropriate for this Collection.

• IllegalArgumentException: if an object cannot be added to this Collection.

• NullPointerException: @throws NullPointerException if collection is null, or if it contains null elements and this Collection does not support such elements.