Sample of Future

main.dart

import 'dart:async';

void main() {
  getAJoke().then((value) {
    print(value);
  })
  .whenComplete(() {
    print('Complete');
  })
  .catchError((error) {
    print('Error');
  });
}
 
Future<String> getAJoke() {
  return new Future<String>.delayed(
    const Duration(seconds: 5), () {
      return "This is a joke";
  });
}