When should I use exceptions vs sealed classes for errors?

Use exceptions for truly unexpected runtime errors (network failures, null references). Use sealed classes (Result ) for expected error conditions that callers should handle explicitly — like API responses that can fail with business logic errors.

Intermediate 7 min readKotlin 2.0

Kotlin Exception Handling — try, catch, finally

Q: Does Kotlin have checked exceptions like Java?

No. Kotlin does not require declaring or catching checked exceptions. All exceptions are unchecked, similar to Java runtime exceptions.

Exceptions handle unexpected errors at runtime. Kotlin uses try/catch/finally, and try can also be used as an expression.

What You Will Learn

Basic try/catch/finally
Catch specific exception types
Use try as an expression
Throw custom exceptions
Kotlin vs Java checked exceptions

Basic try / catch / finally

Wrap risky code in try. Handle errors in catch. finally always runs.

try/catch/finally

kotlin
fun main() {
    try {
        val result = 10 / 0
        println(result)
    } catch (e: ArithmeticException) {
        println("Cannot divide by zero: ${e.message}")
    } finally {
        println("This always runs")
    }
}

Output

Cannot divide by zero: / by zero This always runs

Division by zero throws ArithmeticException. catch catches it and prints the message. finally runs whether or not an exception occurred.

Beginner Tip: finally is used to release resources — close files, database connections, network sockets — regardless of success or failure.

Multiple catch Blocks

Catch different exceptions in separate blocks.

Multiple catch

kotlin
fun parseAndDouble(input: String): Int {
    return try {
        input.toInt() * 2
    } catch (e: NumberFormatException) {
        println("Not a number: $input")
        0
    } catch (e: Exception) {
        println("Unexpected error: ${e.message}")
        -1
    }
}

fun main() {
    println(parseAndDouble("5"))
    println(parseAndDouble("abc"))
}

Output

10 Not a number: abc 0

Specific exceptions are caught first. The general Exception catch is a fallback. try returns a value — the last expression in each branch.

Custom Exceptions

Create custom exception classes by extending Exception.

Custom Exception

kotlin
class InsufficientFundsException(amount: Double) :
    Exception("Insufficient funds: need $${"%.2f".format(amount)}")

fun withdraw(balance: Double, amount: Double): Double {
    if (amount > balance) throw InsufficientFundsException(amount - balance)
    return balance - amount
}

fun main() {
    try {
        val bal = withdraw(100.0, 150.0)
        println("Balance: $bal")
    } catch (e: InsufficientFundsException) {
        println(e.message)
    }
}

Output

Insufficient funds: need $50.00

Custom exceptions extend Exception. throw creates and throws the exception. The message is available via e.message.

Best Practice: Create specific exception types for domain errors. They make catch blocks explicit and improve error messages.

Practice Exercise

Exercisepredict output

What prints? val result = try { "42".toInt() } catch (e: NumberFormatException) { 0 } println(result)

Quick Quiz

Does Kotlin have checked exceptions like Java?

Kotlin Exception Handling — try, catch, finally

What You Will Learn

Basic try / catch / finally

try/catch/finally

Multiple catch Blocks

Multiple catch

Custom Exceptions

Custom Exception

Practice Exercise

Quick Quiz

Frequently Asked Questions

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