Kotlin mapOf

In this guide, we will learn about the Kotlin mapOf() function with lots of examples.

What is mapOf()? 

mapOf() is a Kotlin standard library function that's employed to create an immutable map. A map is essentially a collection of key-value pairs. Once created using mapOf(), the map cannot be modified - meaning no new entries can be added, and existing entries can't be removed or altered. 

Basic Syntax:

val map: Map<KeyType, ValueType> = mapOf(key1 to value1, key2 to value2, ...)

Engaging Examples with Outputs

Creating a Basic Map

val capitalCities = mapOf("France" to "Paris", "Germany" to "Berlin", "Japan" to "Tokyo")
println(capitalCities)  // Output: {France=Paris, Germany=Berlin, Japan=Tokyo}

Accessing Values Using Keys

val fruits = mapOf("a" to "Apple", "b" to "Banana", "c" to "Cherry")
println(fruits["b"])  // Output: Banana

Using Different Data Types for Keys and Values

val data = mapOf(1 to "one", 2 to "two", 3 to "three")
println(data[2])  // Output: two

Empty Map Creation

val emptyMap = mapOf<String, Int>()
println(emptyMap)  // Output: {}

Map with Nullable Values

val scores = mapOf("Alice" to 90, "Bob" to null, "Charlie" to 85)
println(scores["Bob"])  // Output: null

Getting the Size of a Map

val animals = mapOf(1 to "Dog", 2 to "Cat", 3 to "Bird")
println(animals.size)  // Output: 3

Check if a Map contains a specific key or value

Use the containsKey and containsValue functions:

val colors = mapOf("r" to "Red", "g" to "Green", "b" to "Blue")
println(colors.containsKey("g"))  // Output: true
println(colors.containsValue("Purple"))  // Output: false

Convert an immutable Map to a mutable one

val immutableMap = mapOf(1 to "A", 2 to "B")
val mutableVersion = immutableMap.toMutableMap()


In this guide, we understood how to create an immutable Map in Kotlin using mapOf() function. We also saw different operations of Map with examples.