Numbers

Integer types

Kotlin provides a set of built-in types that represent numbers.
For integer numbers, there are four types with different sizes and, hence, value ranges:

Type	Size (bits)	Min value	Max value
`Byte`	8	-128	127
`Short`	16	-32768	32767
`Int`	32	-2,147,483,648 (-2³¹)	2,147,483,647 (2³¹ - 1)
`Long`	64	-9,223,372,036,854,775,808 (-2⁶³)	9,223,372,036,854,775,807 (2⁶³ - 1)

When you initialize a variable with no explicit type specification, the compiler automatically infers the type with the smallest range enough to represent the value starting from Int. If it is not exceeding the range of Int, the type is Int. If it exceeds, the type is Long. To specify the Long value explicitly, append the suffix L to the value. Explicit type specification triggers the compiler to check the value not to exceed the range of the specified type.

val one = 1 // Int
val threeBillion = 3000000000 // Long
val oneLong = 1L // Long
val oneByte: Byte = 1

Floating-point types

For real numbers, Kotlin provides floating-point types Float and Double that adhere to the IEEE 754 standard. Float reflects the IEEE 754 single precision, while Double reflects double precision.

These types differ in their size and provide storage for floating-point numbers with different precision:

Type	Size (bits)	Significant bits	Exponent bits	Decimal digits
`Float`	32	24	8	6-7
`Double`	64	53	11	15-16

You can initialize Double and Float variables with numbers having a fractional part. It's separated from the integer part by a period (.) For variables initialized with fractional numbers, the compiler infers the Double type:

val pi = 3.14 // Double
// val one: Double = 1 // Error: type mismatch
val oneDouble = 1.0 // Double

To explicitly specify the Float type for a value, add the suffix f or F. If such a value contains more than 6-7 decimal digits, it will be rounded:

val e = 2.7182818284 // Double
val eFloat = 2.7182818284f // Float, actual value is 2.7182817

Unlike some other languages, there are no implicit widening conversions for numbers in Kotlin. For example, a function with a Double parameter can be called only on Double values, but not Float, Int, or other numeric values:

fun main() {
    fun printDouble(d: Double) { print(d) }

    val i = 1    
    val d = 1.0
    val f = 1.0f 

    printDouble(d)
//    printDouble(i) // Error: Type mismatch
//    printDouble(f) // Error: Type mismatch
}

To convert numeric values to different types, use explicit conversions.

Literal constants for numbers

There are the following kinds of literal constants for integral values:

Decimals: 123
Longs are tagged by a capital L: 123L
Hexadecimals: 0x0F
Binaries: 0b00001011

Kotlin also supports a conventional notation for floating-point numbers:

Doubles by default: 123.5, 123.5e10
Floats are tagged by f or F: 123.5f

You can use underscores to make number constants more readable:

val oneMillion = 1_000_000
val creditCardNumber = 1234_5678_9012_3456L
val socialSecurityNumber = 999_99_9999L
val hexBytes = 0xFF_EC_DE_5E
val bytes = 0b11010010_01101001_10010100_10010010

Numbers representation on the JVM

On the JVM platform, numbers are stored as primitive types: int, double, and so on. Exceptions are cases when you create a nullable number reference such as Int? or use generics. In these cases numbers are boxed in Java classes Integer, Double, and so on.

Nullable references to the same number can refer to different objects:

fun main() {
//sampleStart
    val a: Int = 100
    val boxedA: Int? = a
    val anotherBoxedA: Int? = a
    
    val b: Int = 10000
    val boxedB: Int? = b
    val anotherBoxedB: Int? = b
    
    println(boxedA === anotherBoxedA) // true
    println(boxedB === anotherBoxedB) // false
//sampleEnd
}

All nullable references to a are actually the same object because of the memory optimization that JVM applies to Integers between -128 and 127. It doesn't apply to the b references, so they are different objects.

On the other hand, they are still equal:

fun main() {
//sampleStart
    val b: Int = 10000
    println(b == b) // Prints 'true'
    val boxedB: Int? = b
    val anotherBoxedB: Int? = b
    println(boxedB == anotherBoxedB) // Prints 'true'
//sampleEnd
}

Explicit number conversions

Due to different representations, smaller types are not subtypes of bigger ones. If they were, we would have troubles of the following sort:

// Hypothetical code, does not actually compile:
val a: Int? = 1 // A boxed Int (java.lang.Integer)
val b: Long? = a // Implicit conversion yields a boxed Long (java.lang.Long)
print(b == a) // Surprise! This prints "false" as Long's equals() checks whether the other is Long as well

So equality would have been lost silently, not to mention identity.

As a consequence, smaller types are NOT implicitly converted to bigger types. This means that assigning a value of type Byte to an Int variable requires an explicit conversion:

val b: Byte = 1 // OK, literals are checked statically
// val i: Int = b // ERROR
val i1: Int = b.toInt()

All number types support conversions to other types:

toByte(): Byte
toShort(): Short
toInt(): Int
toLong(): Long
toFloat(): Float
toDouble(): Double

In many cases, there is no need for explicit conversions because the type is inferred from the context, and arithmetical operations are overloaded for appropriate conversions, for example:

val l = 1L + 3 // Long + Int => Long

Operations on numbers

Kotlin supports the standard set of arithmetical operations over numbers: +, -, *, /, %. They are declared as members of appropriate classes:

fun main() {
//sampleStart
    println(1 + 2)
    println(2_500_000_000L - 1L)
    println(3.14 * 2.71)
    println(10.0 / 3)
//sampleEnd
}

You can also override these operators for custom classes. See Operator overloading for details.

Division of integers

Division between integers numbers always returns an integer number. Any fractional part is discarded.

fun main() {
//sampleStart
    val x = 5 / 2
    //println(x == 2.5) // ERROR: Operator '==' cannot be applied to 'Int' and 'Double'
    println(x == 2)
//sampleEnd
}

This is true for a division between any two integer types:

fun main() {
//sampleStart
    val x = 5L / 2
    println(x == 2L)
//sampleEnd
}

To return a floating-point type, explicitly convert one of the arguments to a floating-point type:

fun main() {
//sampleStart
    val x = 5 / 2.toDouble()
    println(x == 2.5)
//sampleEnd
}

Bitwise operations

Kotlin provides a set of bitwise operations on integer numbers. They operate on the binary level directly with bits of the numbers' representation. Bitwise operations are represented by functions that can be called in infix form. They can be applied only to Int and Long:

val x = (1 shl 2) and 0x000FF000

Here is the complete list of bitwise operations:

shl(bits) – signed shift left
shr(bits) – signed shift right
ushr(bits) – unsigned shift right
and(bits) – bitwise AND
or(bits) – bitwise OR
xor(bits) – bitwise XOR
inv() – bitwise inversion

Floating-point numbers comparison

The operations on floating-point numbers discussed in this section are:

Equality checks: a == b and a != b
Comparison operators: a < b, a > b, a <= b, a >= b
Range instantiation and range checks: a..b, x in a..b, x !in a..b

When the operands a and b are statically known to be Float or Double or their nullable counterparts (the type is declared or inferred or is a result of a smart cast), the operations on the numbers and the range that they form follow the IEEE 754 Standard for Floating-Point Arithmetic.

However, to support generic use cases and provide total ordering, the behavior is different for operands that are not statically typed as floating-point numbers. For example, Any, Comparable<...>, or Collection<T> types. In this case, the operations use the equals and compareTo implementations for Float and Double. As a result:

NaN is considered equal to itself
NaN is considered greater than any other element including POSITIVE_INFINITY
-0.0 is considered less than 0.0

Here is an example that shows the difference in behavior between operands statically typed as floating-point numbers (Double.NaN) and operands not statically typed as floating-point numbers (listOf(T)).

fun main() {
    //sampleStart
    // Operand statically typed as floating-point number
    println(Double.NaN == Double.NaN)                 // false
    // Operand NOT statically typed as floating-point number
    // So NaN is equal to itself
    println(listOf(Double.NaN) == listOf(Double.NaN)) // true

    // Operand statically typed as floating-point number
    println(0.0 == -0.0)                              // true
    // Operand NOT statically typed as floating-point number
    // So -0.0 is less than 0.0
    println(listOf(0.0) == listOf(-0.0))              // false

    println(listOf(Double.NaN, Double.POSITIVE_INFINITY, 0.0, -0.0).sorted())
    // [-0.0, 0.0, Infinity, NaN]
    //sampleEnd
}

Last modified: 25 September 2024