Logical operators

Learn boolean logic with &&, || and !.

Logical operators

Logical operators combine Boolean values: && (and), || (or), ! (not). && yields true when both sides are true. || yields true when at least one side is true. ! flips true to false.

val a = true
val b = false
println(a && b)   // false
println(a || b)   // true
println(!a)        // false

Exercise Try logical

Write a fun main(). Declare val age = 20. Check the age range with println(age >= 18 && age <= 65).

Show example solution

fun main() {
    val age = 20
    println(age >= 18 && age <= 65)
}

Short-circuit evaluation

&& and || are short-circuit operators. In a && b, if a is false, b is not evaluated; the result is already false. In a || b, if a is true, b is not evaluated.

This behavior is especially useful for null checks: x != null && x.length > 0 is safe; if x is null, the second part is not run.

Test yourself

What does `true && false` return?
- true
- null
- false
- It throws an error
Show answer

false — && yields true only when both sides are true.
Logical operators: match the terms

&&

And
||

Or
!

Not
==

Equal

Logical operators: fill in the missing part

val result = (3 > 2) ____ (5 > 10)
println(result)  // true

Show answer

val result = (3 > 2) || (5 > 10)
println(result)  // true

Next lesson: Elvis operator

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