Mutable List Operations in Kotlin

Introduction

Mutable List Operations is a fundamental concept every Kotlin developer should understand. List, Map, and Set are the three core collection types. Choose List for ordered sequences, Set for unique elements, and Map for key-value lookups.

MutableListOf supports add, remove, update and clear operations. In this tutorial you will learn the syntax, walk through a complete example program, study the sample output, and review best practices so you can apply the concept confidently in your own projects.

Definition

• mutableListOf supports add, remove, update and clear operations.
• Changes happen on the same list instance.
• Use when collection content changes at runtime.

Syntax

list.add(item)
list.removeAt(index)

Mutable List Operations in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    val tasks = mutableListOf("Read", "Code")
    tasks.add("Review")
    tasks[1] = "Write Code"
    println(tasks)
}

Sample Output

[Read, Write Code, Review]

When to use

Pick List for ordered data, Set when uniqueness matters, Map when you look up values by a key.

How it works

1. The program starts with a main function — the entry point that runs when you execute the file.

2. val tasks = mutableListOf("Read", "Code") assigns or updates a value used later in the program.

3. tasks[1] = "Write Code" assigns or updates a value used later in the program.

4. The println(tasks) statement writes a line to the console — this produces part of the sample output below.

5. MutableListOf supports add, remove, update and clear operations.

6. Run the program in IntelliJ IDEA, Android Studio, or with the Kotlin command-line compiler (kotlinc / kotlin). Compare your console output with the sample output shown below.

Best Practices

Common Mistakes

Key Points

• mutableListOf supports add, remove, update and clear operations.
• Changes happen on the same list instance.
• Use when collection content changes at runtime.
• Test the example locally and verify the output matches the sample.
• Experiment by changing input values to see how behaviour changes.

Notes

• Semicolons at the end of statements are optional in Kotlin.