Kotlin Operators

Kotlin has a set of operators to perform arithmetic, assignment, comparison operators and more. You will learn to use these operators in this article.

Operators are special symbols (characters) that carry out operations on operands (variables and values). For example, + is an operator that performs addition.

In Java variables article, you learned to declare variables and assign values to variables. Now, you will learn to use operators perform various operations on them.


1. Arithmetic Operators

Here's a list of arithmetic operators in Kotlin:

Kotlin Arithmetic Operators
Operator Meaning
+ Addition (also used for string concatenation)
- Subtraction Operator
* Multiplication Operator
/ Division Operator
% Modulus Operator

Example: Arithmetic Operators

fun main(args: Array<String>) {

    val number1 = 12.5
    val number2 = 3.5
    var result: Double

    result = number1 + number2
    println("number1 + number2 = $result")

    result = number1 - number2
    println("number1 - number2 = $result")

    result = number1 * number2
    println("number1 * number2 = $result")

    result = number1 / number2
    println("number1 / number2 = $result")

    result = number1 % number2
    println("number1 % number2 = $result")
}

When you run the program, the output will be:

number1 + number2 = 16.0
number1 - number2 = 9.0
number1 * number2 = 43.75
number1 / number2 = 3.5714285714285716
number1 % number2 = 2.0

The + operator is also used for the concatenation of String values.


Example: Concatenation of Strings

fun main(args: Array<String>) {

    val start = "Talk is cheap. "
    val middle = "Show me the code. "
    val end = "- Linus Torvalds"

    val result = start + middle + end
    println(result)
}

When you run the program, the output will be:

Talk is cheap. Show me the code. - Linus Torvalds

How arithmetic operators actually work?

Suppose, you are using + arithmetic operator to add two numbers a and b.

Under the hood, the expression a + b calls a.plus(b) member function. The plus operator is overloaded to work with String values and other basic data types (except Char and Boolean).

// + operator for basic types
operator fun plus(other: Byte): Int
operator fun plus(other: Short): Int
operator fun plus(other: Int): Int
operator fun plus(other: Long): Long
operator fun plus(other: Float): Float
operator fun plus(other: Double): Double

// for string concatenation
operator fun String?.plus(other: Any?): String

You can also use + operator to work with user-defined types (like objects) by overloading plus() function.

Recommended Reading: Kotlin Operator Overloading

Here's a table of arithmetic operators and their corresponding functions:

Expression Function name Translates to
a + b plus a.plus(b)
a - b minus a.minus(b)
a * b times a.times(b)
a / b div a.div(b)
a % b mod a.mod(b)

2. Assignment Operators

Assignment operators are used to assign value to a variable. We have already used simple assignment operator = before.

val age = 5

Here, 5 is assigned to variable age using = operator.

Here's a list of all assignment operators and their corresponding functions:

Expression Equivalent to Translates to
a +=b a = a + b a.plusAssign(b)
a += b a = a + b a.minusAssign(b)
a *= b a = a * b a.timesAssign(b)
a /= b a = a / b a.divAssign(b)
a %= b a = a % b a.modAssign(b)

Example: Assignment Operators

fun main(args: Array<String>) {
    var number = 12

    number *= 5   // number = number*5
    println("number  = $number")
}

When you run the program, the output will be:

number = 60

Recommended Reading: Overloading assignment operators in Kotlin.


3. Unary prefix and Increment / Decrement Operators

Here's a table of unary operators, their meaning, and corresponding functions:

Operator Meaning Expression Translates to
+ Unary plus +a a.unaryPlus()
- Unary minus (inverts sign) -a a.unaryMinus()
! not (inverts value) !a a.not()
++ Increment: increases value by1 ++a a.inc()
-- Decrement: decreases value by 1 --a a.dec()

Example: Unary Operators

fun main(args: Array<String>) {
    val a = 1
    val b = true
    var c = 1

    var result: Int
    var booleanResult: Boolean

    result = -a
    println("-a = $result")

    booleanResult = !b
    println("!b = $booleanResult")

    --c
    println("--c = $c")
}

When you run the program, the output will be:

-a = -1
!b = false
--c = 0

Recommended Reading: Overloading Unary Operators


4. Comparison and Equality Operators

Here's a table of equality and comparison operators, their meaning, and corresponding functions:

Operator Meaning Expression Translates to
> greater than a > b a.compareTo(b) > 0
< less than a < b a.compareTo(b) < 0
>= greater than or equals to a >= b a.compareTo(b) >= 0
<= less than or equals to a < = b a.compareTo(b) <= 0
== is equal to a == b a?.equals(b) ?: (b === null)
!= not equal to a != b !(a?.equals(b) ?: (b === null))

Comparison and equality operators are used in control flow such as if expression, when expression, and loops.


Example: Comparison and Equality Operators

fun main(args: Array<String>) {

    val a = -12
    val b = 12

    // use of greater than operator
    val max = if (a > b) {
        println("a is larger than b.")
        a
    } else {
        println("b is larger than a.")
        b
    }

    println("max = $max")
}

When you run the program, the output will be:

b is larger than a.
max = 12

Recommended Reading: Overloading of Comparison and Equality Operators in Kotlin


5. Logical Operators

There are two logical operators in Kotlin: || and &&

Here's a table of logical operators, their meaning, and corresponding functions.

Operator Description Expression Corresponding Function
|| true if either of the Boolean expression is true (a>b)||(a<c) (a>b)or(a<c)
&& true if all Boolean expressions are true (a>b)&&(a<c) (a>b)and(a<c)

Note that, or and and are functions that support infix notation.

Logical operators are used in control flow such as if expression, when expression, and loops.


Example: Logical Operators

fun main(args: Array<String>) {

    val a = 10
    val b = 9
    val c = -1
    val result: Boolean

    // result is true is a is largest
    result = (a>b) && (a>c) // result = (a>b) and (a>c)
    println(result)
}

When you run the program, the output will be:

true

Recommended Reading: Overloading of Logical Operators in Kotlin


6. in Operator

The in operator is used to check whether an object belongs to a collection.

Operator Expression Translates to
in a in b b.contains(a)
!in a !in b !b.contains(a)

Example: in Operator

fun main(args: Array<String>) {

    val numbers = intArrayOf(1, 4, 42, -3)

    if (4 in numbers) {
        println("numbers array contains 4.")
    }
}

When you run the program, the output will be:

numbers array contains 4.

Recommended Reading: Kotlin in Operator Overloading


7. Index access Operator

Here are some expressions using index access operator with corresponding functions in Kotlin.

Expression Translated to
a[i] a.get(i)
a[i, n] a.get(i, n)
a[i1, i2, ..., in] a.get(i1, i2, ..., in)
a[i] = b a.set(i, b)
a[i, n] = b a.set(i, n, b)
a[i1, i2, ..., in] = b a.set(i1, i2, ..., in, b)

Example: Index access Operator

fun main(args: Array<String>) {

    val a  = intArrayOf(1, 2, 3, 4, - 1)
    println(a[1])   
    a[1]= 12
    println(a[1])
}

When you run the program, the output will be:

2
12

Recommended Reading: Kotlin Index access operator Overloading


8. Invoke Operator

Here are some expressions using invoke operator with corresponding functions in Kotlin.

Expression Translated to
a() a.invoke()
a(i) a.invoke(i)
a(i1, i2, ..., in) a.inkove(i1, i2, ..., in)
a[i] = b a.set(i, b)

In Kotlin, parenthesis are translated to call invoke member function.

Recommended Reading: Invoke Operator Overloading in Kotlin


Bitwise Operation

Unlike Java, there are no bitwise and bitshift operators in Kotlin. To perform these task, various functions (supporting infix notation) are used:

  • shl - Signed shift left
  • shr - Signed shift right
  • ushr - Unsigned shift right
  • and - Bitwise and
  • or - Bitwise or
  • xor - Bitwise xor
  • inv - Bitwise inversion

Visit this page to learn more about Bitwise Operations in Kotlin.


Also, there is no ternary operator in Kotlin unlike Java.