main.dart

class Class1 {
  int i = 0;
}

class Class2 extends Class1 {
  
}

void main() {

  Class2 c2 = new Class2();
  Class1 c1 = c2; // Class1 is inherited by Class2. so c1 as Class1 can be a subsitiution of c2

  for (int i = 0; i < 5; i++) {
    print('hello ${c1.i++}');
  }

  print('c2 value ${c2.i}');
}