finally

Learn the cleanup block with finally.

finally

After a try block you can add a finally block. This block always runs, whether or not an error occurred. It is used for cleanup: closing a file, terminating a connection, resetting a flag.

Example: try { open(); process(); } catch (e) { print(e); } finally { close(); }. close() is called both on success and on failure. Even if the error is caught, finally runs before the program continues. You can write code without finally; but adding it is a good habit to avoid leaking resources.

Order: try, catch, finally

The three blocks run in order. First the code inside try runs. If an error occurs catch runs. Finally finally always runs. Even if the error is not caught by catch, finally still runs; then the error propagates up.

A typical pattern: open(), process(), close(). close() belongs in finally so the resource is released even if process() fails. You can put return inside finally but it is not recommended; it overrides a return from try or catch and hurts readability.

Exercise Your turn: cleanup with finally

Declare a String variable message set to "open" at the start. Inside try call int.parse on a non-numeric string. Inside catch (e) set message to "error". Inside finally set message to "closed" and print it.

Show example solution

void main() {
  var message = "open";
  try {
    int.parse("apple");
  } catch (e) {
    message = "error";
  } finally {
    message = "closed";
    print(message);
  }
}

Test yourself

When does the finally block run?
```
try {
  process();
} catch (e) {
  print(e);
} finally {
  close();
}
```
- Always
- Only on error
- Only on success
- Never
Show answer

Only on success — finally always runs; it is independent of error or success.

The finally block

try {
  process();
} catch (e) {
  print(e);
} ____ {
  close();
}

Show answer

try {
  process();
} catch (e) {
  print(e);
} finally {
  close();
}

Match try/catch/finally

try

holds risky code
catch

catches the error
finally

does cleanup
close()

called inside finally

Next lesson: The Exception class

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