Added in API level 24

KeySetView

class KeySetView<K : Any!, V : Any!> : MutableCollection<K>, Serializable, MutableSet<K>

kotlin.Any
↳	java.util.concurrent.ConcurrentHashMap.KeySetView

A view of a ConcurrentHashMap as a Set of keys, in which additions may optionally be enabled by mapping to a common value. This class cannot be directly instantiated. See keySet(V), newKeySet(), newKeySet(int).

Summary

Public methods
Boolean	`add(element: K)` Adds the specified key to this set view by mapping the key to the default mapped value in the backing map, if defined.
Boolean	`addAll(elements: Collection<K>)` Adds all of the elements in the specified collection to this set, as if by calling `add` on each one.
Unit	`clear()` Removes all of the elements from this view, by removing all the mappings from the map backing this view.
Boolean	`contains(element: K)` Returns `true` if this collection contains the specified element.
Boolean	`containsAll(elements: Collection<K>)`
Boolean	`equals(other: Any?)`
Unit	`forEach(action: Consumer<in K>)`
ConcurrentHashMap<K, V>	`getMap()` Returns the map backing this view.
V?	`getMappedValue()` Returns the default mapped value for additions, or `null` if additions are not supported.
Int	`hashCode()`
Boolean	`isEmpty()`
MutableIterator<K>	`iterator()`
Boolean	`remove(element: K)` Removes the key from this map view, by removing the key (and its corresponding value) from the backing map.
Boolean	`removeAll(elements: Collection<K>)`
Boolean	`retainAll(elements: Collection<K>)`
Spliterator<K>	`spliterator()`
Array<Any!>	`toArray()`
Array<T>	`toArray(a: Array<T>)`
String	`toString()` Returns a string representation of this collection.

Properties
Int	`size`

Public methods

add

Added in API level 24

fun add(element: K): Boolean

Adds the specified key to this set view by mapping the key to the default mapped value in the backing map, if defined.

Parameters
`e`	key to be added

Return
`Boolean`	`true` if this set changed as a result of the call

Exceptions
`java.lang.UnsupportedOperationException`	if no default mapped value for additions was provided
`java.lang.ClassCastException`	if the class of the specified element prevents it from being added to this set
`java.lang.NullPointerException`	if the specified key is null
`java.lang.IllegalArgumentException`	if some property of the specified element prevents it from being added to this set
`java.lang.IllegalStateException`	if the element cannot be added at this time due to insertion restrictions

addAll

Added in API level 24

fun addAll(elements: Collection<K>): Boolean

Adds all of the elements in the specified collection to this set, as if by calling add on each one.

Parameters
`c`	the elements to be inserted into this set

Return
`Boolean`	`true` if this set changed as a result of the call

Exceptions
`java.lang.UnsupportedOperationException`	if no default mapped value for additions was provided
`java.lang.ClassCastException`	if the class of an element of the specified collection prevents it from being added to this set
`java.lang.NullPointerException`	if the collection or any of its elements are `null`
`java.lang.IllegalArgumentException`	if some property of an element of the specified collection prevents it from being added to this set
`java.lang.IllegalStateException`	if not all the elements can be added at this time due to insertion restrictions

clear

Added in API level 24

fun clear(): Unit

Removes all of the elements from this view, by removing all the mappings from the map backing this view.

Exceptions
`java.lang.UnsupportedOperationException`	if the `clear` method is not supported by this set

contains

Added in API level 24

fun contains(element: K): Boolean

Returns true if this collection contains the specified element. More formally, returns true if and only if this collection contains at least one element e such that Objects.equals(o, e).

Parameters
`o`	element whose presence in this set is to be tested

Return
`Boolean`	`true` if this set contains the specified element

Exceptions
`java.lang.ClassCastException`	if the type of the specified element is incompatible with this set (optional)
`java.lang.NullPointerException`	if the specified key is null

containsAll

Added in API level 24

fun containsAll(elements: Collection<K>): Boolean

Parameters
`c`	collection to be checked for containment in this set

Return
`Boolean`	`true` if this set contains all of the elements of the specified collection

Exceptions
`java.lang.ClassCastException`	if the types of one or more elements in the specified collection are incompatible with this set (optional)
`java.lang.NullPointerException`	if the specified collection contains one or more null elements and this set does not permit null elements (optional), or if the specified collection is null

equals

Added in API level 24

fun equals(other: Any?): Boolean

Parameters
`obj`	the reference object with which to compare.
`o`	object to be compared for equality with this set

Return
`Boolean`	`true` if the specified object is equal to this set

forEach

Added in API level 24

fun forEach(action: Consumer<in K>): Unit

Parameters
`action`	Consumer<in K>: The action to be performed for each element

Exceptions
`java.lang.NullPointerException`	if the specified action is null

getMap

Added in API level 24

fun getMap(): ConcurrentHashMap<K, V>

Returns the map backing this view.

Return
`ConcurrentHashMap<K, V>`	the map backing this view

getMappedValue

Added in API level 24

fun getMappedValue(): V?

Returns the default mapped value for additions, or null if additions are not supported.

Return
`V?`	the default mapped value for additions, or `null` if not supported

hashCode

Added in API level 24

fun hashCode(): Int

Return
`Int`	the hash code value for this set

isEmpty

Added in API level 24

fun isEmpty(): Boolean

Return
`Boolean`	`true` if this set contains no elements

iterator

Added in API level 24

fun iterator(): MutableIterator<K>

Return
`MutableIterator<K>`	an iterator over the keys of the backing map

remove

Added in API level 24

fun remove(element: K): Boolean

Removes the key from this map view, by removing the key (and its corresponding value) from the backing map. This method does nothing if the key is not in the map.

Parameters
`o`	the key to be removed from the backing map

Return
`Boolean`	`true` if the backing map contained the specified key

Exceptions
`java.lang.ClassCastException`	if the type of the specified element is incompatible with this set (optional)
`java.lang.NullPointerException`	if the specified key is null
`java.lang.UnsupportedOperationException`	if the `remove` operation is not supported by this set

removeAll

Added in API level 24

fun removeAll(elements: Collection<K>): Boolean

Parameters
`c`	collection containing elements to be removed from this set

Return
`Boolean`	`true` if this set changed as a result of the call

Exceptions
`java.lang.UnsupportedOperationException`	if the `removeAll` operation is not supported by this set
`java.lang.ClassCastException`	if the class of an element of this set is incompatible with the specified collection (optional)
`java.lang.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

retainAll

Added in API level 24

fun retainAll(elements: Collection<K>): Boolean

Parameters
`c`	collection containing elements to be retained in this set

Return
`Boolean`	`true` if this set changed as a result of the call

Exceptions
`java.lang.UnsupportedOperationException`	if the `retainAll` operation is not supported by this set
`java.lang.ClassCastException`	if the class of an element of this set is incompatible with the specified collection (optional)
`java.lang.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

spliterator

Added in API level 24

fun spliterator(): Spliterator<K>

Return
`Spliterator<K>`	a `Spliterator` over the elements in this set

toArray

Added in API level 24

fun toArray(): Array<Any!>

Return
`Array<Any!>`	an array containing all the elements in this set

toArray

Added in API level 24

fun <T : Any!> toArray(a: Array<T>): Array<T>

Parameters
`<T>`	the component type of the array to contain the collection
`a`	Array<T>: the array into which the elements of this set are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.

Return
`Array<T>`	an array containing all the elements in this set

Exceptions
`java.lang.ArrayStoreException`	if the runtime type of the specified array is not a supertype of the runtime type of every element in this set
`java.lang.NullPointerException`	if the specified array is null

toString

Added in API level 24

fun toString(): String

Returns a string representation of this collection. The string representation consists of the string representations of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings as by String.valueOf(Object).

Return
`String`	a string representation of this collection

Properties

size

Added in API level 24

val size: Int

Return
`Int`	the number of elements in this set (its cardinality)