Kotlin – Create Custom Exception

Exception handling is an integral part of software development, ensuring that your programs can gracefully handle unexpected situations.

In Kotlin, you can create custom exceptions to provide better error handling for specific scenarios. This article will guide you through the syntax for creating custom exceptions in Kotlin, along with a practical example to illustrate their usage.

Why Create Custom Exceptions ?

Kotlin comes with a comprehensive set of built-in exceptions, which are suitable for most common error situations.

However, there are times when you need to define custom exceptions to accurately represent and manage unique errors within your application. Custom exceptions empower you to specify your own error types, encapsulate specific error details, and maintain clean and understandable code.

Syntax for Creating Custom Exceptions

To create a custom exception in Kotlin, follow these steps:

  1. Define a class that extends either the Exception class or one of its subclasses, depending on the level of specificity required for your exception.
  2. Optionally, create constructors and additional properties or methods to enhance the exception’s functionality and provide relevant context.
  3. Use the throw keyword to throw your custom exception when a specific error condition occurs.

Now, let’s dive into the syntax with a practical example.

Example: Custom Exception for a Payment System

Suppose you’re developing a payment processing system, and you want to handle a scenario where a payment amount is negative. Here’s how you can create and use a custom exception for this situation:

// Step 1: Define a custom exception class
class NegativePaymentAmountException(message: String = "Payment amount cannot be negative") : Exception(message)

// Step 2: Implement a function to process payments
fun processPayment(paymentAmount: Double) {
    // Check if the payment amount is negative
    if (paymentAmount < 0) {
        // Step 3: Throw the custom exception when the amount is negative
        throw NegativePaymentAmountException()

    // Process the payment if the amount is non-negative
    println("Payment processed successfully: $$paymentAmount")

fun main() {
    val amountToPay = -50.0 // Negative payment amount

    try {
        // Step 4: Invoke the function to process the payment
    } catch (e: NegativePaymentAmountException) {
        println("Error: ${e.message}")

In this example:

  • Step 1: We define a custom exception class called NegativePaymentAmountException, which extends the Exception class. The constructor allows you to specify a custom error message (optional but recommended for clarity).
  • Step 2: Inside the processPayment function, we check if the paymentAmount parameter is negative. If it is, we proceed to Step 3.
  • Step 3: We throw the NegativePaymentAmountException when the payment amount is negative, indicating an error condition.
  • Step 4: In the main function, we attempt to process a payment with a negative amount. We catch the NegativePaymentAmountException in a try-catch block and print an error message.

By following this syntax and example, you can create custom exceptions in Kotlin tailored to your application’s unique error scenarios. This approach not only enhances error handling but also makes your code more readable and maintainable.


Exception handling is a critical aspect of software development, ensuring that your applications can gracefully manage errors. Kotlin’s flexibility in creating custom exceptions allows you to address specific error situations effectively.

When designing custom exceptions, use meaningful names and provide informative error messages to enhance code readability and debugging capabilities. Custom exceptions are a powerful tool in your Kotlin toolkit, aiding in the creation of more robust and reliable applications.

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