How to handle exceptions in Kotlin?

Question

I started to learn Kotlin and I can't understand how to handle exceptions. I know there's no checked ones, but anyway, what should I do if my method throws one? For example:

fun test(a: Int, b: Int) : Int {
    return a / b
}

If I divide by zero, I will have ArithmeticException. So how should I handle such things?

Answer 1

ArithmeticException is a runtime exception, so it would be unchecked in Java as well. Your choices for handling it are the same as in Java too:

• Ignore it and get a crash at runtime
• Wrap it with a try-catch block. You catch it anywhere up the stack from where it happens, you don't need any throws declarations.

Since there are no checked exceptions in Kotlin, there isn't a throws keyword either, but if you're mixing Kotlin and Java, and you want to force exception handling of checked exceptions in your Java code, you can annotate your method with a @Throws annotation.

See the official Kotlin docs about exceptions here.

Answer 2

You may write an extension function to return a default value when encounting exception.

fun <T> tryOrDefault(defaultValue: T, f: () -> T): T {
    return try {
        f()
    } catch (e: Exception) {
        defaultValue
    }
}

fun test(a: Int, b: Int) : Int = tryOrDefault(0) {
    a / b
}

Answer 3

You can return Try so that client can call isSuccess or isFailure http://www.java-allandsundry.com/2017/12/kotlin-try-type-for-functional.html

You can also return Int? so that client will know that the value might not exist (when divided by zero).