Finally Block in Dart

Introduction

The finally block always executes after try and catch, regardless of whether an exception was thrown or caught. It is ideal for cleanup code — closing connections, releasing resources, logging completion.

try {
  // risky code
} catch (e) {
  // handle error
} finally {
  // ALWAYS runs
}

Execution Guarantee

void demonstrate(bool throwError) {
  print('Start');
  try {
    if (throwError) throw Exception('Oops!');
    print('No error occurred');
  } catch (e) {
    print('Caught: $e');
  } finally {
    print('Finally always runs');
  }
  print('After try-catch-finally');
}

void main() {
  demonstrate(false);
  print('---');
  demonstrate(true);
}

Start
No error occurred
Finally always runs
After try-catch-finally
---
Start
Caught: Exception: Oops!
Finally always runs
After try-catch-finally

Finally with Return

The finally block runs even when a return statement is encountered inside try:

int divide(int a, int b) {
  try {
    print('Dividing $a by $b');
    return a ~/ b;
  } catch (e) {
    print('Error: $e');
    return -1;
  } finally {
    print('Division attempt complete');  // always prints
  }
}

void main() {
  print(divide(10, 2));   // 5
  print(divide(10, 0));   // -1
}

Resource Cleanup

class DatabaseConnection {
  bool isOpen = false;

  void open() {
    isOpen = true;
    print('Connection opened');
  }

  void close() {
    isOpen = false;
    print('Connection closed');
  }

  List<String> query(String sql) {
    if (!isOpen) throw StateError('Connection is closed');
    return ['row1', 'row2'];
  }
}

void runQuery() {
  var db = DatabaseConnection();
  try {
    db.open();
    var results = db.query('SELECT * FROM users');
    print('Results: $results');
  } catch (e) {
    print('Query failed: $e');
  } finally {
    db.close();  // always closes connection
  }
}

void main() => runQuery();

🧠 Quiz

Summary

The finally block always executes — after try, after catch, even after return. Use it to release resources like database connections, file handles, or network sockets. It runs regardless of whether an exception was thrown or handled.