Kotlin listOfNotNull Function | Create a List Without Null Values in Kotlin

The listOfNotNull function in Kotlin is used to create a list of non-null elements. This function belongs to the Kotlin standard library and provides a straightforward way to filter out null values from a list initialization.

Table of Contents

1. Introduction
2. listOfNotNull Function Syntax
3. Examples
   • Basic Usage
   • Combining Nullable and Non-Nullable Elements
   • Creating a List from a Nullable Collection
4. Real-World Use Case
5. Conclusion

Introduction

The listOfNotNull function is a convenient way to create a list while automatically excluding any null values. This is useful for initializing lists where some elements may be null, and you want to ensure that the resulting list contains only non-null elements.

listOfNotNull Function Syntax

The syntax for the listOfNotNull function is as follows:

fun <T : Any> listOfNotNull(vararg elements: T?): List<T>

Parameters:

• elements: A variable number of elements, which can include null values.

Returns:

• A list containing only the non-null elements from the provided arguments.

Examples

Basic Usage

To demonstrate the basic usage of listOfNotNull, we will create a list with some null values.

Example

fun main() {
    val list = listOfNotNull(1, null, 2, null, 3)
    println("List of non-null values: $list")
}

Output:

List of non-null values: [1, 2, 3]

Combining Nullable and Non-Nullable Elements

This example shows how to use listOfNotNull with a mix of nullable and non-nullable elements.

Example

fun main() {
    val name1: String? = "Alice"
    val name2: String? = null
    val name3: String? = "Bob"

    val names = listOfNotNull(name1, name2, name3)
    println("List of non-null names: $names")
}

Output:

List of non-null names: [Alice, Bob]

Creating a List from a Nullable Collection

This example demonstrates how to create a list from a collection that may contain null values.

Example

fun main() {
    val numbers: List<Int?> = listOf(1, null, 2, null, 3, null)

    val nonNullNumbers = listOfNotNull(*numbers.toTypedArray())
    println("List of non-null numbers: $nonNullNumbers")
}

Output:

List of non-null numbers: [1, 2, 3]

Real-World Use Case

Filtering User Input

In real-world applications, the listOfNotNull function can be used to filter user input or data that may contain null values, ensuring that only valid, non-null data is processed.

Example

fun main() {
    val userInputs: List<String?> = listOf("Alice", null, "Bob", "", null, "Charlie")

    val validInputs = listOfNotNull(*userInputs.toTypedArray()).filter { it.isNotEmpty() }
    println("List of valid inputs: $validInputs")
}

Output:

List of valid inputs: [Alice, Bob, Charlie]

Conclusion

The listOfNotNull function filters out any null values from the provided elements and creates a list containing only the non-null elements. This ensures that the resulting list does not contain any nulls, making it safer to use in situations where null values are not desired.