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Kotlin Booleans


Kotlin Booleans

Very often, in programming, you will need a data type that can only have one of two values, like:

  • YES / NO
  • ON / OFF
  • TRUE / FALSE

For this, Kotlin has a Boolean data type, which can take the values true or false.


Boolean Values

A boolean type can be declared with the Boolean keyword and can only take the values true or false:

Example

val isKotlinFun: Boolean = true
val isFishTasty: Boolean = false
println(isKotlinFun)   // Outputs true
println(isFishTasty)   // Outputs false
Try it Yourself »

Just like you have learned with other data types in the previous chapters, the example above can also be written without specifying the type, as Kotlin is smart enough to understand that the variables are Booleans:

Example

val isKotlinFun = true
val isFishTasty = false
println(isKotlinFun)   // Outputs true
println(isFishTasty)   // Outputs false
Try it Yourself »

Boolean Expression

A Boolean expression returns a Boolean value: true or false.

You can use a comparison operator, such as the greater than (>) operator to find out if an expression (or a variable) is true:

Example

val x = 10
val y = 9
println(x > y) // Returns true, because 10 is greater than 9
Try it Yourself »

Or even easier:

Example

println(10 > 9) // Returns true, because 10 is greater than 9
Try it Yourself »

In the examples below, we use the equal to (==) operator to evaluate an expression:

Example

val x = 10;
println(x == 10); // Returns true, because the value of x is equal to 10
Try it Yourself »

Example

println(10 == 15); // Returns false, because 10 is not equal to 15
Try it Yourself »

The Boolean value of an expression is the basis for all Kotlin comparisons and conditions.

You will learn more about conditions in the next chapter.