Initialize a map in Kotlin

This article explores different ways to initialize a map in Kotlin.

1. Using `mapOf()` function

The mapOf() function returns an unmodifiable map from given key/value pairs, which does not permit subsequent addition or removals.

fun main() {

val immutableMap: Map<String, String> = mapOf(

"Red" to "#FF0000",

"Blue" to "#0000FF"

)

println(immutableMap) // {Red=#FF0000, Blue=#0000FF}

}

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2. Using `mutableMapOf()` function

To get a mutable map of the given key/value pairs, you can use the mutableMapOf() function.

fun main() {

val mutableMap: HashMap<String, String> = mutableMapOf(

"Red" to "#FF0000",

"Blue" to "#0000FF"

) as HashMap<String, String>

println(mutableMap) // {Red=#FF0000, Blue=#0000FF}

}

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3. Using `hashMapOf()` function

To get a Hashmap instance, use hashMapOf() function. If you need LinkedHashMap, use linkedMapOf() function instead.

fun main() {

val hashMap: HashMap<String, String> = hashMapOf(

"Red" to "#FF0000",

"Blue" to "#0000FF"

)

println(hashMap) // {Red=#FF0000, Blue=#0000FF}

}

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4. Using `emptyMap()` function

To get an immutable empty map, consider using emptyMap() function.

fun main() {

val immutableMap: Map<String, String> = emptyMap()

println(immutableMap) // {Red=#FF0000, Blue=#0000FF}

}

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5. Using `Map.of()` function

Java 9 made it very convenient to create a compact, unmodifiable instance of a map by providing static factory methods on the java.util.Map interface.

fun main() {

val immutableMap: Map<String, String> = java.util.Map.of(

"Red", "#FF0000",

"Blue", "#0000FF"

)

println(immutableMap) // {Red=#FF0000, Blue=#0000FF}

}

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6. Using Double Brace Initialization

Another alternative is to use Double Brace Initialization, which creates an anonymous inner class with an instance initializer.

fun main() {

val map: HashMap<String, String> = object : HashMap<String, String>()

{

init {

put("Red", "#FF0000")

put("Blue", "#0000FF")

}

println(map) // {Red=#FF0000, Blue=#0000FF}

}

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That’s all about initializing a map in Kotlin.

Initialize a map in Kotlin

1. Using mapOf() function

2. Using mutableMapOf() function

3. Using hashMapOf() function

4. Using emptyMap() function

5. Using Map.of() function

6. Using Double Brace Initialization

Share this:

1. Using `mapOf()` function

2. Using `mutableMapOf()` function

3. Using `hashMapOf()` function

4. Using `emptyMap()` function

5. Using `Map.of()` function