**Course Title:** Kotlin Programming: From Basics to Advanced Techniques **Section Title:** Error Handling and Exceptions **Topic:** Creating custom exceptions ### Overview In the previous topics, we explored the basics of error handling in Kotlin, including understanding exceptions, try-catch blocks, and finally blocks. However, sometimes the built-in exceptions may not be sufficient to represent specific error conditions in our application. This is where custom exceptions come in handy. In this topic, we will dive into the world of creating custom exceptions in Kotlin. ### Why create custom exceptions? Custom exceptions provide a way to represent specific error conditions that are unique to our application or domain. By creating custom exceptions, we can: * Provide more precise error messages * Handle specific error conditions in a more elegant way * Make our code more readable and maintainable ### Creating custom exceptions In Kotlin, creating a custom exception is a straightforward process. We can define a custom exception class that inherits from the `Exception` class or any of its subclasses. Here is an example of a simple custom exception class: ```kotlin class InsufficientBalanceException(val accountBalance: Double, val amountToWithdraw: Double) : Exception("Insufficient balance to withdraw $amountToWithdraw. Current balance: $accountBalance") ``` In the above example, we have defined a custom exception class `InsufficientBalanceException` that inherits from the `Exception` class. We have also added two properties `accountBalance` and `amountToWithdraw` to represent the specific error condition. ### Throwing custom exceptions Once we have defined our custom exception class, we can throw it using the `throw` keyword. Here is an example of throwing the custom exception: ```kotlin fun withdrawMoney(amountToWithdraw: Double, accountBalance: Double): Double { if (amountToWithdraw > accountBalance) { throw InsufficientBalanceException(accountBalance, amountToWithdraw) } return accountBalance - amountToWithdraw } ``` In the above example, we have a function `withdrawMoney` that takes two parameters `amountToWithdraw` and `accountBalance`. We check if the `amountToWithdraw` is greater than the `accountBalance`. If it is, we throw the `InsufficientBalanceException`. ### Catching custom exceptions To catch custom exceptions, we can use the `try-catch` block. Here is an example of catching the custom exception: ```kotlin fun main() { try { val newBalance = withdrawMoney(1000.0, 500.0) println("Withdrawal successful. New balance: $newBalance") } catch (e: InsufficientBalanceException) { println("Error: ${e.message}") } } ``` In the above example, we have a `main` function where we call the `withdrawMoney` function within a `try-catch` block. We catch the `InsufficientBalanceException` and print the error message. ### Key takeaways * Custom exceptions provide a way to represent specific error conditions in our application * We can define custom exception classes that inherit from the `Exception` class or any of its subclasses * We can throw custom exceptions using the `throw` keyword * We can catch custom exceptions using the `try-catch` block ### Conclusion In this topic, we explored the concept of creating custom exceptions in Kotlin. We learned how to define custom exception classes, throw custom exceptions, and catch custom exceptions. By creating custom exceptions, we can make our code more readable, maintainable, and efficient. If you have any questions or need further clarification, please feel free to leave a comment. We will cover best practices for error handling in the next topic. For more information on Kotlin programming, you can refer to the official Kotlin documentation: [https://kotlinlang.org/docs/](https://kotlinlang.org/docs/) Exercise: Create a custom exception class for a specific error condition in your application. How would you handle this exception?