Variables in Kotlin

A variable is a named area in memory used to store and process data. A variable in Kotlin always has a name, a data type and a value. The name of the variable is a freely selectable identifier that can consist of alphanumeric characters or underscores and must begin with either a letter or an underscore. To define a variable in Kotlin you can use two keywords val or var should be used.

The syntax for defining a variable in Kotlin is as follows:

val|var variable_name: variable_type

A variable is defined by first using the keyword val or var is used, followed by the variable name and a colon after which the variable type is specified. 

In the example below, variable age with the type Int (for integer values ​​without decimal places) declared:

    val age: Int

The next step, a value is assigned to the variable age:

fun main() {
    val age: Int
    age = 25
}

In the final statement, the assigned value is output using the function println ():

fun main() {
    val age: Int // Declaration of the variable age
    age = 25     // Assignment of value 25
    println(age) // Output assigned variable value using println() function
}

Immutable and mutable variables

There are two types of variables in Kotlin: immutable and mutable. Immutable variables are created using the keyword val declared and can only be initialized once with a value. Attempting to change the value of a val variable will produce a compilation error.

fun main() {
    val age: Int 
    age = 25     // The first value assignment works without any problems
    age = 52     // An error occurs when attempting to assign a different value
    println(age)
}

Mutable variables are declared with the keyword var and can be updated multiple times with different values ​​during the runtime of the program.

fun main() {
    var age: Int 
    age = 25     // First value assignment
    println(age)
    age = 52     // Change of the value
    println(age)  
}

Exercises for this chapter →