Add Multiple Elements to ArrayList in Kotlin | Kotlin ArrayList addAll Function

The addAll function in Kotlin is used to add all elements from a specified collection to an ArrayList. This function is part of the Kotlin standard library and provides a convenient way to add multiple elements to an ArrayList at once.

Table of Contents

1. Introduction
2. addAll Function Syntax
3. Examples
   • Basic Usage
   • Adding Elements from Another List
   • Adding Elements at a Specific Index
4. Real-World Use Case
5. Conclusion

Introduction

The addAll function allows you to add all elements from a specified collection to an ArrayList. This is useful for scenarios where you need to combine multiple collections or extend an existing collection with additional elements.

addAll Function Syntax

The syntax for the addAll function is as follows:

1. To add all elements from a specified collection to the end of the list:

fun <T> ArrayList<T>.addAll(elements: Collection<T>): Boolean

2. To add all elements from a specified collection starting at a specified index:

fun <T> ArrayList<T>.addAll(index: Int, elements: Collection<T>): Boolean

Parameters:

• elements: The collection of elements to be added to the list.
• index (optional): The position at which the elements should be added.

Returns:

• Boolean: Returns true if the list was modified as a result of the operation.

The addAll function appends all elements from the specified collection to the end of the list or inserts them starting at a specified index. If you specify an index, the elements are inserted at that index, and subsequent elements are shifted to the right.

Examples

Basic Usage

To demonstrate the basic usage of addAll, we will add elements from one ArrayList to another and print the resulting list.

Example

fun main() {
    val numbers1 = arrayListOf(1, 2, 3)
    val numbers2 = arrayListOf(4, 5, 6)
    numbers1.addAll(numbers2)
    println("Numbers: $numbers1")
}

Output:

Numbers: [1, 2, 3, 4, 5, 6]

Adding Elements from Another List

This example shows how to add elements from another list to an ArrayList.

Example

fun main() {
    val fruits = arrayListOf("Apple", "Banana")
    val moreFruits = listOf("Cherry", "Date")
    fruits.addAll(moreFruits)
    println("Fruits: $fruits")
}

Output:

Fruits: [Apple, Banana, Cherry, Date]

Adding Elements at a Specific Index

This example demonstrates how to add elements from another list starting at a specific index in an ArrayList.

Example

fun main() {
    val colors = arrayListOf("Red", "Green", "Blue")
    val moreColors = listOf("Yellow", "Orange")
    colors.addAll(1, moreColors)
    println("Colors: $colors")
}

Output:

Colors: [Red, Yellow, Orange, Green, Blue]

Real-World Use Case

Combining Multiple Lists of Tasks

In real-world applications, the addAll function can be used to combine multiple lists of tasks, allowing users to manage and organize tasks efficiently.

Example

data class Task(val id: Int, val description: String)

fun main() {
    val tasks1 = arrayListOf(
        Task(1, "Do the laundry"),
        Task(2, "Buy groceries")
    )
    val tasks2 = listOf(
        Task(3, "Write blog post"),
        Task(4, "Clean the house")
    )
    tasks1.addAll(tasks2)
    println("Tasks: $tasks1")
}

Output:

Tasks: [Task(id=1, description=Do the laundry), Task(id=2, description=Buy groceries), Task(id=3, description=Write blog post), Task(id=4, description=Clean the house)]

Conclusion

The addAll function in Kotlin is a simple and effective way to add multiple elements to an ArrayList at once. It allows you to dynamically manage collections by adding elements from other collections, either at the end of the list or starting at a specific position. 

By understanding and using the addAll function, you can effectively manage and manipulate ArrayList collections in your Kotlin applications.