stdlib/kotlin.collections/Map

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

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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interface Entry<out K, out V>

Represents a key/value pair held by a Map.

Since Kotlin 1.0

Functions

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abstract fun containsKey(key: K): Boolean

Returns true if the map contains the specified key.

Since Kotlin 1.0
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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
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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
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abstract fun isEmpty(): Boolean

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

Since Kotlin 1.0

Properties

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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
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abstract val keys: Set<K>

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

Since Kotlin 1.0
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abstract val size: Int

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

Since Kotlin 1.0
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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

Inheritors

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Extensions

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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
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inline fun <K, V> Map<out K, V>.maxWith(comparator: Comparator<in Map.Entry<K, V>>): Map.Entry<K, V>?
Since Kotlin 1.0
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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
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fun <K, V> Map<out K, V>.minWith(comparator: Comparator<in Map.Entry<K, V>>): Map.Entry<K, V>?
Since Kotlin 1.0
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inline fun Map<String, String>.toProperties(): Properties

Converts this Map to a Properties object.

Since Kotlin 1.0
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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