Custom exceptions
- Kotlin course
- Beginner
- Lesson 104/116
- 5 min
Learn to write custom exception classes in Kotlin.
Custom exceptions: your own error class
You can define your own class for application-specific errors. It inherits from a generic exception type; you pass the message to the constructor.
class TaskError(message: String) : Exception(message)
throw TaskError("Task not found")The class name explains the error clearly. You can also choose RuntimeException instead of Exception. A custom type makes both catching and debugging easier.
Throwing and catching custom exceptions
You throw your class with throw and catch it with catch. The type name shows which error is caught.
try {
throw TaskError("Not found")
} catch (e: TaskError) {
println(e.message)
}catch (e: TaskError) only catches this type. You can set up different catch blocks for different error types. This keeps error handling tidy and meaningful.
Practice Define the TaskError class
Define the class TaskError(message: String) : Exception(message). Write fun find(id: Int) that throws TaskError("Task not found: $id"). In main call find(99); catch TaskError and print e.message.
Starter code
fun main() {
// Define an error class, throw it in a function, catch in main and print
}Sample solution
class TaskError(message: String) : Exception(message)
fun find(id: Int) {
throw TaskError("Task not found: $id")
}
fun main() {
try {
find(99)
} catch (e: TaskError) {
println(e.message)
}
}Expected output
Görev bulunamadı: 99
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Fill in the blank: superclass
class TaskError(message: String) : ____(message)class TaskError(message: String) : Exception(message)Explanation: Exception is used as the superclass.
2 Why define a custom exception?
- For less memory
- To write less code
- For speed
- For more meaningful error types Correct answer
Explanation: Application-specific error types are more meaningful.
3 Match part to role
| Term | Meaning |
|---|---|
class TaskError |
Class definition |
: Exception |
Superclass |
throw TaskError |
Throwing |
catch (e: TaskError) |
Catching |