kotlin-stdlib / kotlin.collections / Map

Map

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interface Map<K, out V>
(Common source) (Native 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.

Parameters

K - 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.

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

Types

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Entry

Represents a key/value pair held by a Map.

interface Entry<out K, out V>

Properties

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entries

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

abstract val entries: Set<Entry<K, V>>
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keys

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

abstract val keys: Set<K>
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size

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

abstract val size: Int
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values

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

abstract val values: Collection<V>

Functions

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containsKey

Returns true if the map contains the specified key.

abstract fun containsKey(key: K): Boolean
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containsValue

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

abstract fun containsValue(value: V): Boolean
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get

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

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

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

open fun getOrDefault(key: K, defaultValue: V): V
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isEmpty

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

abstract fun isEmpty(): Boolean

Extension Functions

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all

Returns true if all entries match the given predicate.

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

Returns true if map has at least one entry.

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

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

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

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

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

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

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

Checks if the map contains the given key.

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

Returns true if the map contains the specified key.

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

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

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

Returns the number of entries in this map.

fun <K, V> Map<out K, V>.count(): Int

Returns the number of entries matching the given predicate.

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

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

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

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

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

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

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

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

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

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

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

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

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

Returns the first non-null value produced by transform function being applied to entries of this map in iteration order, or throws NoSuchElementException if no non-null value was produced.

fun <K, V, R : Any> Map<out K, V>.firstNotNullOf(
    transform: (Entry<K, V>) -> R?
): R
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firstNotNullOfOrNull

Returns the first non-null value produced by transform function being applied to entries of this map in iteration order, or null if no non-null value was produced.

fun <K, V, R : Any> Map<out K, V>.firstNotNullOfOrNull(
    transform: (Entry<K, V>) -> R?
): R?
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flatMap

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

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

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

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

Performs the given action on each entry.

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

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

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

Returns the value to which the specified key is mapped, or defaultValue if this map contains no mapping for the key.

fun <K, V> Map<out K, V>.getOrDefault(
    key: K,
    defaultValue: V
): V
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getOrElse

Returns the value for the given key if the value is present and not null. Otherwise, returns the result of the defaultValue function.

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

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

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

Returns the value for the given key or throws an exception if there is no such key in the map.

fun <K, V> Map<K, V>.getValue(key: K): V
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isNotEmpty

Returns true if this map is not empty.

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

Returns true if this nullable map is either null or empty.

fun <K, V> Map<out K, V>?.isNullOrEmpty(): Boolean
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iterator

Returns an Iterator over the entries in the Map.

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

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

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

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.

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

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.

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

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

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

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

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

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

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

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.

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

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.

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

Returns the first entry yielding the largest value of the given function or null if there are no entries.

fun <K, V, R : Comparable<R>> Map<out K, V>.maxByOrNull(
    selector: (Entry<K, V>) -> R
): Entry<K, V>?
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maxOf

Returns the largest value among all values produced by selector function applied to each entry in the map.

fun <K, V> Map<out K, V>.maxOf(
    selector: (Entry<K, V>) -> Double
): Double
fun <K, V> Map<out K, V>.maxOf(
    selector: (Entry<K, V>) -> Float
): Float
fun <K, V, R : Comparable<R>> Map<out K, V>.maxOf(
    selector: (Entry<K, V>) -> R
): R
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maxOfOrNull

Returns the largest value among all values produced by selector function applied to each entry in the map or null if there are no entries.

fun <K, V> Map<out K, V>.maxOfOrNull(
    selector: (Entry<K, V>) -> Double
): Double?
fun <K, V> Map<out K, V>.maxOfOrNull(
    selector: (Entry<K, V>) -> Float
): Float?
fun <K, V, R : Comparable<R>> Map<out K, V>.maxOfOrNull(
    selector: (Entry<K, V>) -> R
): R?
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maxOfWith

Returns the largest value according to the provided comparator among all values produced by selector function applied to each entry in the map.

fun <K, V, R> Map<out K, V>.maxOfWith(
    comparator: Comparator<in R>,
    selector: (Entry<K, V>) -> R
): R
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maxOfWithOrNull

Returns the largest value according to the provided comparator among all values produced by selector function applied to each entry in the map or null if there are no entries.

fun <K, V, R> Map<out K, V>.maxOfWithOrNull(
    comparator: Comparator<in R>,
    selector: (Entry<K, V>) -> R
): R?

maxWith

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Returns the first entry having the largest value according to the provided comparator.

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

Returns the first entry having the largest value according to the provided comparator or null if there are no entries.

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

Returns the first entry yielding the smallest value of the given function or null if there are no entries.

fun <K, V, R : Comparable<R>> Map<out K, V>.minByOrNull(
    selector: (Entry<K, V>) -> R
): Entry<K, V>?
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minOf

Returns the smallest value among all values produced by selector function applied to each entry in the map.

fun <K, V> Map<out K, V>.minOf(
    selector: (Entry<K, V>) -> Double
): Double
fun <K, V> Map<out K, V>.minOf(
    selector: (Entry<K, V>) -> Float
): Float
fun <K, V, R : Comparable<R>> Map<out K, V>.minOf(
    selector: (Entry<K, V>) -> R
): R
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minOfOrNull

Returns the smallest value among all values produced by selector function applied to each entry in the map or null if there are no entries.

fun <K, V> Map<out K, V>.minOfOrNull(
    selector: (Entry<K, V>) -> Double
): Double?
fun <K, V> Map<out K, V>.minOfOrNull(
    selector: (Entry<K, V>) -> Float
): Float?
fun <K, V, R : Comparable<R>> Map<out K, V>.minOfOrNull(
    selector: (Entry<K, V>) -> R
): R?
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minOfWith

Returns the smallest value according to the provided comparator among all values produced by selector function applied to each entry in the map.

fun <K, V, R> Map<out K, V>.minOfWith(
    comparator: Comparator<in R>,
    selector: (Entry<K, V>) -> R
): R
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minOfWithOrNull

Returns the smallest value according to the provided comparator among all values produced by selector function applied to each entry in the map or null if there are no entries.

fun <K, V, R> Map<out K, V>.minOfWithOrNull(
    comparator: Comparator<in R>,
    selector: (Entry<K, V>) -> R
): R?
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minus

Returns a map containing all entries of the original map except the entry with the given key.

operator fun <K, V> Map<out K, V>.minus(key: K): Map<K, V>

Returns a map containing all entries of the original map except those entries the keys of which are contained in the given keys collection.

operator fun <K, V> Map<out K, V>.minus(
    keys: Iterable<K>
): Map<K, V>

Returns a map containing all entries of the original map except those entries the keys of which are contained in the given keys array.

operator fun <K, V> Map<out K, V>.minus(
    keys: Array<out K>
): Map<K, V>

Returns a map containing all entries of the original map except those entries the keys of which are contained in the given keys sequence.

operator fun <K, V> Map<out K, V>.minus(
    keys: Sequence<K>
): Map<K, V>

minWith

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Returns the first entry having the smallest value according to the provided comparator.

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

Returns the first entry having the smallest value according to the provided comparator or null if there are no entries.

fun <K, V> Map<out K, V>.minWithOrNull(
    comparator: Comparator<in Entry<K, V>>
): Entry<K, V>?
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none

Returns true if the map has no entries.

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

Returns true if no entries match the given predicate.

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

Performs the given action on each entry and returns the map itself afterwards.

fun <K, V, M : Map<out K, V>> M.onEach(
    action: (Entry<K, V>) -> Unit
): M
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onEachIndexed

Performs the given action on each entry, providing sequential index with the entry, and returns the map itself afterwards.

fun <K, V, M : Map<out K, V>> M.onEachIndexed(
    action: (index: Int, Entry<K, V>) -> Unit
): M
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orEmpty

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

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

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

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 entries to this map from a given collection of key-value pairs.

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 array of key-value pairs.

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 sequence of key-value pairs.

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 another map.

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

Returns a List containing all key-value pairs.

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

Returns a new read-only map containing all key-value pairs from the original map.

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

Populates and returns the destination mutable map with key-value pairs from the given map.

fun <K, V, M : MutableMap<in K, in V>> Map<out K, V>.toMap(
    destination: M
): M
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toMutableMap

Returns a new mutable map containing all key-value pairs from the original map.

fun <K, V> Map<out K, V>.toMutableMap(): MutableMap<K, V>
JVM
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toProperties

Converts this Map to a Properties object.

fun Map<String, String>.toProperties(): Properties
JVM
1.0

toSortedMap

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

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 the sorting order provided by the given comparator.

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

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

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

Inheritors

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AbstractMap

Provides a skeletal implementation of the read-only Map interface.

abstract class AbstractMap<K, out V> : Map<K, V>
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MutableMap

A modifiable 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.

interface MutableMap<K, V> : Map<K, V>