finally
- Kotlin course
- Beginner
- Lesson 102/116
- 5 min
Learn the cleanup block with finally.
finally: the always-run block
The finally block always runs, whether or not an error occurs. It is ideal for closing resources or cleanup.
try {
val x = 10 / 0
} catch (e: ArithmeticException) {
println("Error")
} finally {
println("Done")
}
// Error, DoneEven with an error, finally runs; that makes it safe for closing files or databases. It can be written without catch; then it only does cleanup. finally cannot be skipped.
finally and resource cleanup
After opening a resource you must close it. finally guarantees this even if an error occurs.
var open = true
try {
// use resource
} finally {
open = false // always close
}With or without an error, open = false runs. This prevents resource leaks. Even a return inside try still triggers the close in finally.
Practice Set up try-catch-finally
Inside a try block write val x = 10 / 0. Catch ArithmeticException and print "Error". Then in a finally block print "Done".
Starter code
fun main() {
// Wrap a block in try-catch-finally; print Error and Done
}Sample solution
fun main() {
try {
val x = 10 / 0
} catch (e: ArithmeticException) {
println("Error")
} finally {
println("Done")
}
}Expected output
Hata Bitti
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match block to job
| Term | Meaning |
|---|---|
try |
Trial block |
catch |
Error catching |
finally |
Always runs |
throw |
Error raising |
2 Fill in the blank: write finally
try {
val x = 1
} ____ {
println("Done")
}try {
val x = 1
} finally {
println("Done")
}Explanation: the finally block always runs.
3 When does finally run?
- Only when an error occurs
- Always Correct answer
- Only when no error
- Never
Explanation: finally runs whether or not there is an error.