Map

interface Map<K, out V>(source)

A collection that holds pairs of objects (keys and values) and supports efficiently retrieving the value corresponding to each key. Map keys are unique; the map holds only one value for each key. Methods in this interface support only read-only access to the map; read-write access is supported through the MutableMap interface.

Since Kotlin

1.0

Parameters

the type of map keys. The map is invariant in its key type, as it can accept key as a parameter (of containsKey for example) and return it in keys set.

the type of map values. The map is covariant in its value type.

Inheritors

MutableMap

Types

Entry

interface Entry<out K, out V>

Represents a key/value pair held by a Map.

Since Kotlin 1.0

Properties

entries

abstract val entries: Set<Map.Entry<K, V>>

Returns a read-only Set of all key/value pairs in this map.

Since Kotlin 1.0

keys

abstract val keys: Set<K>

Returns a read-only Set of all keys in this map.

Since Kotlin 1.0

size

abstract val size: Int

Returns the number of key/value pairs in the map.

Since Kotlin 1.0

values

abstract val values: Collection<V>

Returns a read-only Collection of all values in this map. Note that this collection may contain duplicate values.

Since Kotlin 1.0

Functions

all

inline fun <K, V> Map<out K, V>.all(predicate: (Map.Entry<K, V>) -> Boolean): Boolean

Returns true if all entries match the given predicate.

Since Kotlin 1.0

any

fun <K, V> Map<out K, V>.any(): Boolean

Returns true if map has at least one entry.

Since Kotlin 1.0

inline fun <K, V> Map<out K, V>.any(predicate: (Map.Entry<K, V>) -> Boolean): Boolean

Returns true if at least one entry matches the given predicate.

Since Kotlin 1.0

asIterable

inline fun <K, V> Map<out K, V>.asIterable(): Iterable<Map.Entry<K, V>>

Creates an Iterable instance that wraps the original map returning its entries when being iterated.

Since Kotlin 1.0

asSequence

fun <K, V> Map<out K, V>.asSequence(): Sequence<Map.Entry<K, V>>

Creates a Sequence instance that wraps the original map returning its entries when being iterated.

Since Kotlin 1.0

contains

inline operator fun <K, V> Map<out K, V>.contains(key: K): Boolean

Checks if the map contains the given key.

Since Kotlin 1.0

containsKey

abstract fun containsKey(key: K): Boolean

Returns true if the map contains the specified key.

Since Kotlin 1.0

containsKey

inline fun <K> Map<out K, *>.containsKey(key: K): Boolean

Returns true if the map contains the specified key.

Since Kotlin 1.0

containsValue

abstract fun containsValue(value: @UnsafeVariance V): Boolean

Returns true if the map maps one or more keys to the specified value.

Since Kotlin 1.0

containsValue

inline fun <K, V> Map<K, V>.containsValue(value: V): Boolean

Returns true if the map maps one or more keys to the specified value.

Since Kotlin 1.0

count

inline fun <K, V> Map<out K, V>.count(): Int

Returns the number of entries in this map.

Since Kotlin 1.0

inline fun <K, V> Map<out K, V>.count(predicate: (Map.Entry<K, V>) -> Boolean): Int

Returns the number of entries matching the given predicate.

Since Kotlin 1.0

filter

inline fun <K, V> Map<out K, V>.filter(predicate: (Map.Entry<K, V>) -> Boolean): Map<K, V>

Returns a new map containing all key-value pairs matching the given predicate.

Since Kotlin 1.0

filterKeys

inline fun <K, V> Map<out K, V>.filterKeys(predicate: (K) -> Boolean): Map<K, V>

Returns a map containing all key-value pairs with keys matching the given predicate.

Since Kotlin 1.0

filterNot

inline fun <K, V> Map<out K, V>.filterNot(predicate: (Map.Entry<K, V>) -> Boolean): Map<K, V>

Returns a new map containing all key-value pairs not matching the given predicate.

Since Kotlin 1.0

filterNotTo

inline fun <K, V, M : MutableMap<in K, in V>> Map<out K, V>.filterNotTo(destination: M, predicate: (Map.Entry<K, V>) -> Boolean): M

Appends all entries not matching the given predicate into the given destination.

Since Kotlin 1.0

filterTo

inline fun <K, V, M : MutableMap<in K, in V>> Map<out K, V>.filterTo(destination: M, predicate: (Map.Entry<K, V>) -> Boolean): M

Appends all entries matching the given predicate into the mutable map given as destination parameter.

Since Kotlin 1.0

filterValues

inline fun <K, V> Map<out K, V>.filterValues(predicate: (V) -> Boolean): Map<K, V>

Returns a map containing all key-value pairs with values matching the given predicate.

Since Kotlin 1.0

flatMap

inline fun <K, V, R> Map<out K, V>.flatMap(transform: (Map.Entry<K, V>) -> Iterable<R>): List<R>

Returns a single list of all elements yielded from results of transform function being invoked on each entry of original map.

Since Kotlin 1.0

flatMapTo

inline fun <K, V, R, C : MutableCollection<in R>> Map<out K, V>.flatMapTo(destination: C, transform: (Map.Entry<K, V>) -> Iterable<R>): C

Appends all elements yielded from results of transform function being invoked on each entry of original map, to the given destination.

Since Kotlin 1.0

forEach

inline fun <K, V> Map<out K, V>.forEach(action: (Map.Entry<K, V>) -> Unit)

Performs the given action on each entry.

Since Kotlin 1.0

get

abstract operator fun get(key: K): V?

Returns the value corresponding to the given key, or null if such a key is not present in the map.

Since Kotlin 1.0

get

inline operator fun <K, V> Map<out K, V>.get(key: K): V?

Returns the value corresponding to the given key, or null if such a key is not present in the map.

Since Kotlin 1.0

getOrElse

inline fun <K, V> Map<K, V>.getOrElse(key: K, defaultValue: () -> V): V

Returns the value for the given key, or the result of the defaultValue function if there was no entry for the given key.

Since Kotlin 1.0

getValue

inline operator fun <V, V1 : V> Map<in String, V>.getValue(thisRef: Any?, property: KProperty<*>): V1

Returns the value of the property for the given object from this read-only map.

Since Kotlin 1.0

isEmpty

abstract fun isEmpty(): Boolean

Returns true if the map is empty (contains no elements), false otherwise.

Since Kotlin 1.0

isNotEmpty

inline fun <K, V> Map<out K, V>.isNotEmpty(): Boolean

Returns true if this map is not empty.

Since Kotlin 1.0

iterator

inline operator fun <K, V> Map<out K, V>.iterator(): Iterator<Map.Entry<K, V>>

Returns an Iterator over the entries in the Map.

Since Kotlin 1.0

map

inline fun <K, V, R> Map<out K, V>.map(transform: (Map.Entry<K, V>) -> R): List<R>

Returns a list containing the results of applying the given transform function to each entry in the original map.

Since Kotlin 1.0

mapKeys

inline fun <K, V, R> Map<out K, V>.mapKeys(transform: (Map.Entry<K, V>) -> R): Map<R, V>

Returns a new Map with entries having the keys obtained by applying the transform function to each entry in this Map and the values of this map.

Since Kotlin 1.0

mapKeysTo

inline fun <K, V, R, M : MutableMap<in R, in V>> Map<out K, V>.mapKeysTo(destination: M, transform: (Map.Entry<K, V>) -> R): M

Populates the given destination map with entries having the keys obtained by applying the transform function to each entry in this Map and the values of this map.

Since Kotlin 1.0

mapNotNull

inline fun <K, V, R : Any> Map<out K, V>.mapNotNull(transform: (Map.Entry<K, V>) -> R?): List<R>

Returns a list containing only the non-null results of applying the given transform function to each entry in the original map.

Since Kotlin 1.0

mapNotNullTo

inline fun <K, V, R : Any, C : MutableCollection<in R>> Map<out K, V>.mapNotNullTo(destination: C, transform: (Map.Entry<K, V>) -> R?): C

Applies the given transform function to each entry in the original map and appends only the non-null results to the given destination.

Since Kotlin 1.0

mapTo

inline fun <K, V, R, C : MutableCollection<in R>> Map<out K, V>.mapTo(destination: C, transform: (Map.Entry<K, V>) -> R): C

Applies the given transform function to each entry of the original map and appends the results to the given destination.

Since Kotlin 1.0

mapValues

inline fun <K, V, R> Map<out K, V>.mapValues(transform: (Map.Entry<K, V>) -> R): Map<K, R>

Returns a new map with entries having the keys of this map and the values obtained by applying the transform function to each entry in this Map.

Since Kotlin 1.0

mapValuesTo

inline fun <K, V, R, M : MutableMap<in K, in R>> Map<out K, V>.mapValuesTo(destination: M, transform: (Map.Entry<K, V>) -> R): M

Populates the given destination map with entries having the keys of this map and the values obtained by applying the transform function to each entry in this Map.

Since Kotlin 1.0

maxBy

inline fun <K, V, R : Comparable<R>> Map<out K, V>.~~maxBy~~(selector: (Map.Entry<K, V>) -> R): Map.Entry<K, V>?

Since Kotlin 1.0

maxWith

inline fun <K, V> Map<out K, V>.~~maxWith~~(comparator: Comparator<in Map.Entry<K, V>>): Map.Entry<K, V>?

Since Kotlin 1.0

minBy

inline fun <K, V, R : Comparable<R>> Map<out K, V>.~~minBy~~(selector: (Map.Entry<K, V>) -> R): Map.Entry<K, V>?

Since Kotlin 1.0

minWith

fun <K, V> Map<out K, V>.~~minWith~~(comparator: Comparator<in Map.Entry<K, V>>): Map.Entry<K, V>?

Since Kotlin 1.0

none

fun <K, V> Map<out K, V>.none(): Boolean

Returns true if the map has no entries.

Since Kotlin 1.0

inline fun <K, V> Map<out K, V>.none(predicate: (Map.Entry<K, V>) -> Boolean): Boolean

Returns true if no entries match the given predicate.

Since Kotlin 1.0

orEmpty

inline fun <K, V> Map<K, V>?.orEmpty(): Map<K, V>

Returns the Map if its not null, or the empty Map otherwise.

Since Kotlin 1.0

plus

operator fun <K, V> Map<out K, V>.plus(pairs: Array<out Pair<K, V>>): Map<K, V>

Creates a new read-only map by replacing or adding entries to this map from a given array of key-value pairs.

Since Kotlin 1.0

operator fun <K, V> Map<out K, V>.plus(pair: Pair<K, V>): Map<K, V>

Creates a new read-only map by replacing or adding an entry to this map from a given key-value pair.

Since Kotlin 1.0

operator fun <K, V> Map<out K, V>.plus(pairs: Iterable<Pair<K, V>>): Map<K, V>

Creates a new read-only map by replacing or adding entries to this map from a given collection of key-value pairs.

Since Kotlin 1.0

operator fun <K, V> Map<out K, V>.plus(map: Map<out K, V>): Map<K, V>

Creates a new read-only map by replacing or adding entries to this map from another map.

Since Kotlin 1.0

operator fun <K, V> Map<out K, V>.plus(pairs: Sequence<Pair<K, V>>): Map<K, V>

Creates a new read-only map by replacing or adding entries to this map from a given sequence of key-value pairs.

Since Kotlin 1.0

toList

fun <K, V> Map<out K, V>.toList(): List<Pair<K, V>>

Returns a List containing all key-value pairs.

Since Kotlin 1.0

toProperties

inline fun Map<String, String>.toProperties(): Properties

Converts this Map to a Properties object.

Since Kotlin 1.0

toSortedMap

fun <K : Comparable<K>, V> Map<out K, V>.toSortedMap(): SortedMap<K, V>

Converts this Map to a SortedMap. The resulting SortedMap determines the equality and order of keys according to their natural sorting order.

Since Kotlin 1.0

fun <K, V> Map<out K, V>.toSortedMap(comparator: Comparator<in K>): SortedMap<K, V>

Converts this Map to a SortedMap. The resulting SortedMap determines the equality and order of keys according to the sorting order provided by the given comparator.

Since Kotlin 1.0

withDefault

fun <K, V> Map<K, V>.withDefault(defaultValue: (key: K) -> V): Map<K, V>

Returns a wrapper of this read-only map, having the implicit default value provided with the specified function defaultValue.

Since Kotlin 1.0

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