How to Use Variables and Constants in Kotlin

Kotlin is a powerful language developed in accordance with modern programming needs and is used on many platforms, especially for Android applications. Variables and constants in Kotlin are the building blocks for storing data in your program. In this article, we will technically discuss how variables and constants are defined in Kotlin, their differences, and usage examples.

How to Define Variables in Kotlin?

Variables in Kotlin are defined with two keywords: var and val. The content of variables defined with the var keyword can be changed, while the value of those defined with val cannot be changed after the initial assignment.

Defining Variables with Var

var ad: String = "Ali"
ad = "Veli" // Valid, because 'ad' is a var variable

Defining Constants with Val

val yil: Int = 2024
yil = 2025 // Gives an error: Variables defined with val cannot be changed

As we see in the examples above, while the value of the variable "ad" defined with var can be changed, the compiler gives an error if you try to assign a new value to the variable "yil" defined with val. Thanks to variables and constants in Kotlin, our code becomes more readable and error-free.

Kotlin Constants and Best Practices

In Kotlin, val is generally used to define constants. However, for compile time constants, the const val keyword is used. If the value of the constant is definitively known at compile time, you should prefer this.

const val PI: Double = 3.1415926535

The const val keyword can only be used outside of objects (at the top-level or inside companion objects). Within functions, only val can be used for defining constants. Understanding the concept of variables and constants in Kotlin correctly increases the data integrity and code safety of your application.

Conclusion

In summary, in Kotlin, variables and constants are defined using the keywords var, val, and const val for storing data. For mutable data, use var; for immutable ones, use val; and for those that must be constant at compile time, use const val as best practice. When you learn the details about variables and constants in Kotlin, you can write safer and more sustainable code.