Default Parameter in Kotlin : Predefined Values

Kotlin has many modern features. One such powerful feature is default parameter in Kotlin, which enables developers to define function parameters with predefined values.

This capability allows for greater Coe flexibility, increased readability, and reduced redundancy. We will delve into the concept of default parameter in Kotlin.

Default Parameter

Default parameter in Kotlin provide the ability to assign default values to function parameters. This means that when a function is called, parameters can be omitted, and the default values specified in the function declaration will be used instead.

This feature makes it easier to work with functions that have a large number of parameters or allows for optional arguments in functions calls.

Defining Default Parameters

In Kotlin, default parameters are defined directly in the function declaration. To assign a default value to a parameter, simply provide it after the parameter’s type, followed by an equals sign and the default value.

fun greet(name: String = "Guest", message: String = "Hello") {
    println("$message, $name!")
}

In the above code snippet, the function greet has two parameters, name and message, both of which have default values assigned. If these parameters are not provided when calling the function, the default values will be used.

Kotlin : Overriding Default Parameters

Although default parameters provide convenience, Kotlin allows developers to override them by explicitly providing values for any desired parameter. This flexibility enables fine-grained control over the behaviour of functions without sacrificing simplicity.

Open the Kotlin playground and write the following code.

fun greet(name: String = "Guest", message: String = "Hello") {
    println("$message, $name!")
}

fun main() {
    greet() // Prints "Hello, Guest!"
    greet("Nikin") // Prints "Hello, Nikin!"
    greet(message = "Good morning") // Prints "Good morning, Guest!"
    greet("Nikin", "Good evening") // Prints "Good evening, Nikin!"
}

Hello, Guest!
Hello, Nikin!
Good morning, Guest!
Good evening, Nikin!

Benefits of Default Parameters

Default parameters simplify function calls by reducing the need for repetitive parameter values. Developers can focus on the necessary arguments and avoid cluttering their code with redundant information.

Reduced Function Overloads : In traditional languages, providing different versions of a function with varying parameter lists is a common practice. Kotlin’s default parameters eliminate the need for excessive function overloads, leading to cleaner codebases with fewer duplicate functions.

Area of a circle using a default parameter for the radius

import kotlin.math.PI

fun calculateCircleArea(radius: Double = 1.0): Double {
    return PI * radius * radius
}

fun main() {
    val radius1 = 3.0
    val radius2 = 5.0

    val area1 = calculateCircleArea(radius1)
    val area2 = calculateCircleArea(radius2)

    println("The area of a circle with radius $radius1 is $area1")
    println("The area of a circle with radius $radius2 is $area2")
}

Output

The area of a circle with radius 3.0 is 28.274333882308138
The area of a circle with radius 5.0 is 78.53981633974483

Default parameters in Kotlin are a powerful feature that simplifies code by providing predefined values for function parameters. They improve code readability, reduce the need for function overloads, ensure backward compatibility, and enhance API design.