finally and Guaranteed Cleanup
Run code whether or not it throws.
finally and Guaranteed Cleanup is a free Dart Academy lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Dart Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Cleanup Must Always Run
Open files and connections must be closed even if code fails. Dart gives you finally for cleanup that always happens. 🧹
The finally Block
A finally block runs after try and catch, no matter what. Success or failure, its code always executes.
try {
work();
} finally {
cleanup();
}Runs After Success
If the try block finishes with no error, Dart still runs finally right afterward before moving on.
Runs After a Catch
When an exception is caught, the catch block runs, then finally runs too. Both fire, in that order.
try {
fail();
} catch (e) {
log(e);
} finally {
close();
}Runs Even Without a Catch
Use try with only finally, no catch. The exception still propagates, but cleanup runs first on its way out.
try {
risky();
} finally {
release();
}Why Not Just Duplicate?
Without finally, you would copy cleanup into both success and error paths. One finally block keeps it in a single place.
Cleanup Before Re-throw
Even when an exception keeps bubbling up uncaught, finally still runs first, so resources never leak.
Closing a File Safely
A classic use: open a resource in try, use it, then finally close it whether or not reading succeeded.
try {
file.read();
} finally {
file.close();
}Avoid Returning in finally
A return inside finally overrides any earlier return or exception. Keep finally for cleanup only, not control flow.
Order of Execution
Remember the sequence: try runs, then catch if needed, then finally last. Cleanup always closes out the block.
Full try-catch-finally
This combines all three: guarded work, error handling, and guaranteed finally cleanup at the end.
try {
open();
} catch (e) {
print(e);
} finally {
close();
}Quick Check
When does a finally block run?
Recap
You now use finally for guaranteed cleanup that runs on every path: success, caught error, or uncaught throw. No leaks. 🔒
Frequently asked questions
Is the “finally and Guaranteed Cleanup” lesson free?
Yes — the full text of “finally and Guaranteed Cleanup” is free to read here on the web, and the Dart Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Dart Academy course, upgrade to CoddyKit PRO.
What will I learn in “finally and Guaranteed Cleanup”?
Run code whether or not it throws. You practise Dart Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Dart Academy?
No prior experience is required. Dart Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “finally and Guaranteed Cleanup” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Dart Academy lesson?
Yes. Every Dart Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- throw, try, and catch
- on Clauses and Exception Types
- finally and Guaranteed Cleanup
- Custom Exceptions and rethrow