Data Types

Data types are a classification of types of data that determine possible values and operations that can be performed on that data.

Kotlin has primitive and non-primitive data types:

Primitive Data Types

There are the following different types of primitive data types in Kotlin:

  • Boolean
  • Byte
  • Char
  • Double
  • Float
  • Int
  • Long
  • Short

Boolean

In Kotlin, Boolean can hold either true or false. To declare a boolean variable, the var or val keyword can be used, followed by the variable name, and the assigned boolean value:

val isTrue: Boolean = true
val isFalse: Boolean = false

A boolean can be used to determine the outcome of if...else statements:

fun main(){
val condition: Boolean = true
if (condition) {
// Code that gets executed if the variable is true
} else {
// Code that gets executed if the variable is false
}
}

Byte

A Byte is a data type that is similar to an integer data type, but it is only 8 bits in size. While an integer can be a different size depending on the system, a byte can only hold values from -128 to 127.

Bytes are commonly used to store small pieces of data, such as characters in a text file or colors in an image.

Here is an example of how to declare a byte variable in Kotlin:

fun main() {
val a: Byte = 50
val b: Byte = 25
val c: Byte = a + b as Byte
print(c)
}

The output will be:

75

Calculations that exceed the byte range will produce unexpected results:

fun main() {
val a: Byte = 120
val b: Byte = 120
val c: Byte = a + b as Byte
print(c)
}

The expected output is 240, but since that exceeds the range for a byte, the output will be:

-88

Char

Char represents a primitive data type that can hold any character from the Unicode character set, which includes letters, digits, symbols, and special characters.

Here is an example of how to declare a character variable in Kotlin:

val ch: Char = 'A'

Double

Double represents a 64-bit floating-point number. It is a primitive data type that can hold values with a fractional component, such as 3.14 or 0.5.

Here is an example of how to declare a double variable in Kotlin:

fun main() {
val a: Double = 3.14
val b: Double = 2.71
val c: Double = a * b as Double
print(c)
}

The output of the above code will be:

8.5094

In this example, c will be assigned the value 8.5014, which is the result of 3.14 * 2.71.

A double can be used to perform more advanced operations, such as calculating the square root of a number or raising a number to the power of another number. For example:

import kotlin.math.sqrt
import kotlin.math.pow
fun main() {
val a: Double = 16.0
val b: Double = sqrt(a)
val c: Double = a.pow(2)
println("The square root of $a is $b.")
println("$a raised to the power of 2 is $c.")
}

The output will be:

The square root of 16.0 is 4.0.
16.0 raised to the power of 2 is 256.0.

Float

Float represents a 32-bit floating-point number. It is a primitive data type that can hold values with a fractional component, such as 3.14 or 0.5.

Here is an example of how to declare a float in Kotlin:

fun main() {
val a: Float = 3.14f
val b: Float = 2.71f
val c: Float = a * b as Float
print(c)
}

The output will be:

8.5094

In this example, c will be assigned the value 8.5014, which is the result of 3.14 * 2.71.

Int

Int represents a 32-bit signed integer. It is a primitive data type that can hold values ranging from -2147483648 to 2147483647.

Here is an example of how to declare an integer variable in Kotlin:

fun main() {
val a: Int = 50
val b: Int = 25
val c: Int = a + b
print(c)
}

The output of the above code will be:

75

Long

Long represents a 64-bit signed integer. It is a primitive data type that can hold values ranging from -9223372036854775808 to 9223372036854775807.

Here is an example of how to declare a long variable in Kotlin:

fun main() {
val a: Long = 500000000
val b: Long = 250000000
val c: Long = a + b
print(c)
}

The output for the above code will be:

750000000

In this example, c will be assigned the value 750000000, which is the result of 500000000 + 250000000.

Short

Short represents a 16-bit signed integer. It is a primitive data type that can hold values ranging from -32768 to 32767.

Here is an example of how to declare a short variable in Kotlin:

fun main() {
val a: Short = 50
val b: Short = 25
val c: Short = (a + b).toShort()
print(c)
}

The output for the above code will be:

75

In this example, the c variable will be assigned the value 75, which is the result of 50 + 25. The toShort() function is used to convert the result to a Short type.

Non-Primitive Data Types

The following are non-primitive data types in Kotlin:

  • Any
  • Arrays
  • Class
  • Enum
  • List
  • Map
  • Nothing
  • Set
  • String
  • Unit

Arrays

An Array is a data structure that stores a fixed-size collection of elements of the same data type. They are non-primitive data types, which means they are derived from primitive data types or other non-primitive data types.

To declare an array in Kotlin, the arrayOf() function can be utilized, with the elements of the array specified within the parentheses. For instance:

fun main() {
val numbers: Array<Int> = arrayOf(1, 2, 3, 4, 5)
}

In this example, the numbers variable is an array of integers that contains some numberical values. The type of the array is specified using the Array<Int> syntax, which indicates that the array contains elements of the Int type.

String

In Kotlin, a String is a data type that represents a sequence of characters. A string can be used to store and manipulate text in a program.

Here is an example of how to declare and initialize a string in Kotlin:

fun main() {
val message: String = "Hello, World!"
print(message)
}

The output for the above code will be:

Hello, World!

Strings are also immutable in Kotlin.

The + operator can be used to concatenate strings or the trim() function to remove leading and trailing whitespace from a string. For example:

fun main() {
val greeting: String = "Hello, "
val name: String = "John"
val fullMessage: String = greeting + name
println(fullMessage.trim())
}

The output for the above code will be:

Hello, John

Any

In Kotlin, the Any type is a supertype of all types in the language. It represents a general type that can hold any value.

Here is an example of how to declare a variable of type Any in Kotlin:

fun main() {
val value: Any = 100
val value2: Any = "Hello, World!"
println(value)
println(value2)
}

The output for the above code will be:

100
Hello, World!

Nothing

Nothing is a special type that represents the absence of a value. It is a subtype of all types in the language and cannot be instantiated.

The Nothing type is used to indicate that a function never returns a value. For example, a function that throws an exception or terminates the program will have a return type of Nothing.

Here is an example of a function that has a return type of Nothing:

fun error(): Nothing {
throw IllegalStateException("An error occurred.")
}

In the above, the error() function throws an exception and does not return a value, therefore, its return type is Nothing.

Unit

In Kotlin, Unit is another special type that represents the absence of a value. It’s similar to Void in other programming languages and is used to indicate that a function does not return a value. Unit is also a subtype of Any which means that it can be used in place of any type.

The Unit type can be used to specify that a function has a return type of Unit when it is not possible to infer the return type from the function’s body. For example:

fun doSomething(): Unit {
// Perform some action here
}

In the above example, the doSomething() function performs some action and does not return a value. Therefore, its return type is Unit.

Contributors

Interested in helping build Docs? Read the Contribution Guide or share your thoughts in this feedback form.

Learn Kotlin on Codecademy