Client and backend. This class is shared: the same code is compiled into your app and into your server, so everything on this page works in both.

public static class ConcurrentHashMap.KeySetView<K, V>

  1. Object
  2. AbstractCollection<K>
  3. AbstractSet<K>
  4. ConcurrentHashMap.KeySetView

ImplementsCollection<K>, Iterable<K>, Serializable, Set<K>

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.

Methods

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

Inherited methods

From AbstractSet

equals, hashCode, removeAll

From AbstractCollection

containsAll, retainAll, toString, toArray, toArray

From Object

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

From Collection

removeIf, stream, parallelStream, spliterator, toArray

From Iterable

forEach

From Set

of, of, of, of, of, of, of, of, of, of, of, of, copyOf

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()

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.

size

public int size()

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

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

Returns

true if this Collection has no elements, false otherwise.

See also

contains

public boolean contains(Object o)
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

o 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
if the object to look for is null and this Collection doesn’t support null elements.

remove

public boolean remove(Object o)
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

o Object
the object to remove.

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
if object is null and this Collection doesn’t support null elements.

clear

public void clear()

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
it the iterator does not support removing elements from this Collection

See also

add

public boolean add(K e)

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

e K
the object to add.

Returns

true if this Collection is modified, false otherwise.

Throws

UnsupportedOperationException
if adding to this Collection is not supported.
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)

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

c Collection<? extends K>
the collection of objects.

Returns

true if this Collection is modified, false otherwise.

Throws

UnsupportedOperationException
if adding to this Collection is not supported.
ClassCastException
if the class of an object is inappropriate for this Collection.
IllegalArgumentException
if an object cannot be added to this Collection.
NullPointerException
if collection is null, or if it contains null elements and this Collection does not support such elements.