Initialize a Map using the explicit constructor or via the syntactic sugar with curly braces. You must specify both the Key type and the Value type.

// 1. Explicit Constructor
val explicitMap = Map<String, Int>()
println("Is empty? ${if (explicitMap.isEmpty()) "Yes" else "No"}")

// 2. Sugar Syntax
val inventory = <String, Int>{"Apple": 10, "Banana": 20, "Cherry": 30}

println("Size is: ${inventory.size()}") // 3

Accessing & Modifying

Use set() to add or update pairs. Use get() to retrieve values — it returns an optional type (V?) that is null when the key doesn't exist.

val m = <String, Int>{"Apple": 10}

// Retrieve a value (m["Apple"] == m.get("Apple"))
println(m["Apple"])   // 10
println(m["Durian"])  // null

// Update an existing key (m["Apple"] = 15 == m.set("Apple", 15))
m["Apple"] = 15

// Check if a key exists
val hasCherry = m.containsKey("Cherry") // false

// Remove a key-value pair
m.remove("Apple")
m.clear() // Empties the entire map

Iteration & Views

Iterate over the Map using forEach() with a closure. Extract all keys or all values into separate Arrays using keys() and values().

val numMap = <Int, Int>{1: 100, 2: 200, 3: 300}

// Iterate using a single-expression closure
numMap.forEach {|key, value| println("Key: ${key}, Value: ${value}") }

// Iterate using a block-body closure
var total = 0
numMap.forEach {|key, value| -> {
    total = total + value
}}
println("Sum of all values: ${total}")

// Extract Keys and Values into Arrays
val keysArr = numMap.keys()     // [1, 2, 3]
val valuesArr = numMap.values() // [100, 200, 300]

Methods Reference

Modification

set(key: K, value: V) — Inserts a new pair or updates the value if the key already exists.
remove(key: K) — Removes the key and its corresponding value.
clear() — Removes all key-value pairs.

Querying

get(key: K): V? — Returns the value or null if the key does not exist.
getOrDefault(key: K, defaultValue: V): V — Returns the value or a fallback default.
containsKey(key: K): Bool — Returns true if the Map contains the specified key.
size(): Int — Returns the total number of key-value pairs.
isEmpty(): Bool — Returns true if the Map contains 0 items.

Iteration & Utility

forEach(fn: (K, V) -> Void) — Executes a closure once for each key-value pair.
keys(): Array<K> — Returns a new Array containing all keys.
values(): Array<V> — Returns a new Array containing all values.
toString(): String — Returns a string representation of the Map.

← PreviousSet Next →Bytes