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Kotlin Operators

An operator is a sign that compares values or combines truth values. A comparison gives true or false as its result.

Comparing numbers

Each comparison gives true or false. The printed answers show each result in order.

fun main() {
    println(7 > 3)
    println(7 < 3)
    println(7 == 7)
}

Equal strings

Two strings with the same letters are equal. A different spelling gives a different answer.

fun main() {
    println("apple" == "apple")
    println("apple" == "apply")
    println("apple" != "apply")
}

Both sides with &&

The && sign needs both sides to be true. One false side makes the whole result false.

fun main() {
    val sunny = true
    val warm = false
    println(sunny && warm)
    println(sunny && true)
}

At least one side with ||

The || sign needs only one true side. It gives false only when both sides are false.

fun main() {
    val sunny = true
    val warm = false
    println(sunny || warm)
    println(warm || false)
}

Flipping with !

The ! sign flips a Boolean value. True becomes false and false becomes true.

fun main() {
    val ready = false
    println(!ready)
    println(ready)
}

Example

fun main() {
    val score = 75
    val passed = score >= 50
    println(passed)
    println(passed && score < 100)
    println(!passed || score == 75)
}

Key points

  • ==: checks whether two values are equal.
  • !=: checks whether two values are different.
  • < and >: compare size between two values.
  • <= and >=: compare size and allow equality.
  • &&: gives true only when both sides are true.
  • ||: gives true when at least one side is true.
  • !: flips true to false and false to true.

In this example, score holds 75. passed holds true because score >= 50 is true. The first print shows true. The second print joins passed with score < 100 and shows true. The third print flips passed and joins it with score == 75, and the right side makes the result true.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Kotlin Playground

Exercise

What does println(5 <= 5) print?