Kotlin throw Exception Tutorial With Example

In this kotlin tutorial, we will learn how to use kotlin throw keyword in exception. Why is throw keyword used?
How is throw keyword used? etc.

throw keyword is used to throw an exception explicitly. It is also used to throw a custom exception.

Syntax of throw keyword

throw ExceptionName("Some message")

Kotlin throw example

Let’s see an example to use throw keyword –

fun main(args: Array<String>) {
    validate(15)
    println("code after age validation check")
}

fun validate(age: Int) {
    if (age < 18)
        throw ArithmeticException("You are under age")
    else
        println("Eligible to vote in India")
}

When you run the above program, you will output –
Exception in thread “main” java.lang.ArithmeticException: You are under age

Notice how we used throw keyword to throw ArithmeticException explicitly.

In kotlin, throw construct is an expression and can combine with other expressions as well.

Examples of throw as an expression

fun main(args: Array<String>) {
    val letter = 'c'
    val result =
            if (letter in 'a'..'z')
                letter
            else
                throw IllegalArgumentException("A letter must be between a to z")

    print(result)
}

When you run the program, you will get output as below –
c

Exercises on throw in kotlin

1. Guess the output of below program,

fun main(args: Array<String>) {
    val letter = '1'
    val result =
            if (letter in 'a'..'z')
                letter
            else
                throw IllegalArgumentException("A letter must be between a to z")

    print(result)
}

2. Guess the output of below program

fun main(args: Array<String>) {
    val letter = '111'
    val result =
            if (letter in 'a'..'z')
                letter
            else
                throw IllegalArgumentException("A letter must be between a to z")

    print(result)
}

3. Guess the output of below program

fun main(args: Array<String>) {
    val letter = 'S'
    val result =
            if (letter in 'a'..'z')
                letter
            else
                throw IllegalArgumentException("A letter must be between a to z")

    print(result)
}

That’s end of tutorial on kotlin throw exception tutorial.