How to Add a Key-Value Pair to a Map in Kotlin

How to Add a Key-Value Pair to a Map in Kotlin ?

Answer

To add a key-value pair to a map in Kotlin, you can use the plus operator or the put method.

✐ Examples

1 Adding a Key-Value Pair Using plus Operator

We can add a key-value pair to an immutable map in Kotlin using the plus operator, which returns a new map with the specified key and value added.

For example,

We start by declaring and initializing an immutable map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We use the plus operator to add a new key-value pair to the map. The plus operator returns a new map with the specified key and value added.
We print the updated map to the console using a for loop and println.

Kotlin Program

fun main() {
    // Declare and initialize an immutable map
    val myMap = mapOf(
        "one" to 1,
        "two" to 2,
        "three" to 3
    )

    // Add a key-value pair using plus operator
    val updatedMap = myMap + ("four" to 4)

    // Print the updated map
    for ((key, value) in updatedMap) {
        println("$key: $value")
    }
}

Output

one: 1
two: 2
three: 3
four: 4

2 Adding a Key-Value Pair Using put Method

We can add a key-value pair to a mutable map in Kotlin using the put method, which associates the specified value with the specified key in the map.

For example,

We start by declaring and initializing a mutable map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We use the put method to add a new key-value pair to the map. The put method takes two arguments: the key and the value to be added.
We print the updated map to the console using a for loop and println.

Kotlin Program

fun main() {
    // Declare and initialize a mutable map
    val myMap = mutableMapOf(
        "one" to 1,
        "two" to 2,
        "three" to 3
    )

    // Add a key-value pair using put method
    myMap.put("four", 4)

    // Print the updated map
    for ((key, value) in myMap) {
        println("$key: $value")
    }
}

Output

one: 1
two: 2
three: 3
four: 4

3 Adding Multiple Key-Value Pairs Using putAll Method

We can add multiple key-value pairs to a mutable map in Kotlin using the putAll method, which adds all key-value pairs from another map.

For example,

We start by declaring and initializing a mutable map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We use the putAll method to add multiple new key-value pairs to the map. The putAll method takes another map containing the key-value pairs to be added.
We print the updated map to the console using a for loop and println.

Kotlin Program

fun main() {
    // Declare and initialize a mutable map
    val myMap = mutableMapOf(
        "one" to 1,
        "two" to 2,
        "three" to 3
    )

    // Add multiple key-value pairs using putAll method
    myMap.putAll(mapOf("four" to 4, "five" to 5))

    // Print the updated map
    for ((key, value) in myMap) {
        println("$key: $value")
    }
}

Output

one: 1
two: 2
three: 3
four: 4
five: 5

Summary

In this tutorial, we learned How to Add a Key-Value Pair to a Map in Kotlin language with well detailed examples.

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