@ovveride

void main() {
  TimesTwo tt = TimesTwo(2);
  print(tt.calculate());
  
  TimesFour tf = TimesFour(2);
  print(tf.calculate());
}

class TimesTwo {
  final int number;
  
  TimesTwo(
    this.number,
  );
  
  int calculate() {
    return number * 2;
  }
}

class TimesFour extends TimesTwo {
  TimesFour(
    int number,
  ): super(number);
  
  @override
  int calculate() {
    return super.calculate() * 2;
  }
}