Why is it necessary to use abstract fields in classes?

Abstract fields are necessary for defining the interface of a class, requiring concrete subclasses to provide their implementation. This ensures uniform data structure for various implementations.

abstract class Shape {
  abstract double area; // Abstract field for area

  void draw(); // Abstract method
}

class Circle extends Shape {
  double radius;

  Circle(this.radius);

  @override
  double get area => 3.14 * radius * radius; // Implementation of abstract field

  @override
  void draw() {
    print('Drawing a circle');
  }
}