Add Items to a List in Kotlin

  1. Use the + Operator to Add Items to a List in Kotlin
  2. Use the plus Method to Add Items to a List in Kotlin
  3. Use the Add() Method to Add Items to a List in Kotlin

Suppose you have created a list in Kotlin. After making a list, you realize that you need to add more items. How will you do that?

This article lists different ways to add items to a list in Kotlin with some easy-to-digest examples.

Use the + Operator to Add Items to a List in Kotlin

The first and easiest way to add more items to a list is using the + operator. Using this operator returns the original list along with the newly added items.

We can use this operator to add both single elements and an entire collection. Below are a couple of examples where we use the + operator to add items to a list.

The first example has a car list with the names of some popular cars. We will use the + operator to add a single new item to the list.

Example:

fun main() {
    val cars = listOf("Mercedes-Benz", "Porsche", "BMW")
    val modified = cars + ("Ferrari")
    println(modified)
}

Output:

Use + Operator to Add a Single Item to a List

We will use the same operator to add another list with three more names of car brands to our existing list.

Example:

fun main() {
    val cars = listOf("Mercedes-Benz", "Porsche", "BMW")
    val newList = listOf("Ferrari", "Lamborghini", "Bentley")
    val modified = cars + newList
    println(modified)
}

Output:

Use + Operator to Add a List to a List

Use the plus Method to Add Items to a List in Kotlin

Another way to add items to a list is using the plus method. Like the + operator, we can add a single item and a collection to a list.

As examples for this one, we will create a list of fruits and add new elements.

Example :

fun main() {
    val fruits = listOf("Apple", "Mango", "Strawberry")
    val modified = fruits + ("Pineapple")
    println(modified)
}

Output:

Use the plus Method to Add a Single Item to a List

Example :

fun main() {
    val fruits = listOf("Apple", "Mango", "Strawberry")
    val newList = listOf("Pineapple", "Orange", "Blueberries")
    val modified = fruits.plus(newList)
    println(modified)
}

Output:

Use the plus Method to Add a List to a List

Use the Add() Method to Add Items to a List in Kotlin

Another method that allows adding items to a list is the add() method.

However, the list needs to be mutable for this method to work. If we try using the add() method with a standard list, it will throw an error.

Example:

fun main() {
    val myList = listOf("One", "Two", "Three")
    myList.add("Four")
    println(myList)
}

Output:

Use the add Method With a Standard List

As we can see, trying to add items to a standard list throws an error. Hence, we can add items only to a mutable list using the add() method.

We can create a mutable list using mutableListOf<T>. Here’s an example of adding the word Four to the list.

Example:

fun main() {
    val myList = mutableListOf("One", "Two", "Three")
    myList.add("Four")
    println(myList)
}

Output:

Use the add Method With a Mutable List

The catch with using the add() method is that we can only add a single item to a list with this method. If we try to add a list, it will throw a type mismatch error.

Example:

fun main() {
    val myList = mutableListOf("One", "Two", "Three")
    val newList = mutableListOf("Four", "Five", "Six")
    myList.add(newList)
    println(myList)
}

Output:

Use the add Method With a Mutable List to Add Another List

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