Traditional Usage of if...else
The syntax of if...else is:
if (testExpression) {
// codes to run if testExpression is true
}
else {
// codes to run if testExpression is false
}
if executes a certain section of code if the testExpression is evaluated to true. It can have optional else clause. Codes inside else clause are executed if the testExpression is false.
Example: Traditional Usage of if...else
fun main(args: Array<String>) {
val number = -10
if (number > 0) {
print("Positive number")
} else {
print("Negative number")
}
}
When you run the program, the output will be:
Negative number
Kotlin if expression
Unlike Java (and other many programming languages), if can be used an expression in Kotlin; it returns a value. Recommended Reading: Kotlin expression
Here is an example:
Example: Kotin if expression
fun main(args: Array<String>) {
val number = -10
val result = if (number > 0) {
"Positive number"
} else {
"Negative number"
}
println(result)
}
When you run the program, the output will be:
Negative number
The else branch is mandatory when using if as an expression.
The curly braces are optional if the body of if has only one statement. For example,
fun main(args: Array<String>) {
val number = -10
val result = if (number > 0) "Positive number" else "Negative number"
println(result)
}
This is similar to ternary operator in Java. Hence, there is no ternary operator in Kotlin.
Example: if block With Multiple Expressions
If the block of if branch contains more than one expression, the last expression is returned as the value of the block.
fun main(args: Array<String>) {
val a = -9
val b = -11
val max = if (a > b) {
println("$a is larger than $b.")
println("max variable holds value of a.")
a
} else {
println("$b is larger than $a.")
println("max variable holds value of b.")
b
}
println("max = $max")
}
When you run the program, the output will be:
-9 is larger than -11. max variable holds value of a. max = -9
Recommended Reading: Kotlin when Statement
Kotlin if..else..if Ladder
You can return a block of code among many blocks in Kotlin using if..else...if ladder.
Example: if...else...if Ladder
fun main(args: Array<String>) {
val number = 0
val result = if (number > 0)
"positive number"
else if (number < 0)
"negative number"
else
"zero"
println("number is $result")
}
This program checks whether number is positive number, negative number, or zero.
Kotlin Nested if Expression
An if expression can be inside the block of another if expression known as nested if expression.
Example: Nested if Expression
This program computes the largest number among three numbers.
fun main(args: Array<String>) {
val n1 = 3
val n2 = 5
val n3 = -2
val max = if (n1 > n2) {
if (n1 > n3)
n1
else
n3
} else {
if (n2 > n3)
n2
else
n3
}
println("max = $max")
}
When you run the program, the output will be:
max = 5