डिज़ाइन

public class Main {
  // Minimal API sketch to validate the design
  static abstract class Shape {
    abstract double area();
    abstract double perimeter();
  }

  static class Circle extends Shape {
    double radius;
    Circle(double r) { radius = r; }
    double area() { return Math.PI * radius * radius; }
    double perimeter() { return 2 * Math.PI * radius; }
  }

  public static void main(String[] args) {
    Shape s = new Circle(2.0);
    System.out.println("area=" + s.area());
    System.out.println("perimeter=" + s.perimeter());
  }
}

public class Main {
  static abstract class Shape {
    abstract double area();
    abstract double perimeter();
    String info() {
      // default helper for neat printing
      return String.format("area=%.2f, per=%.2f", area(), perimeter());
    }
  }
  static class Circle extends Shape {
    double radius;
    Circle(double r) { radius = r; }
    double area() { return Math.PI * radius * radius; }
    double perimeter() { return 2 * Math.PI * radius; }
    public String toString() { return "Circle " + info(); }
  }
  static class Rectangle extends Shape {
    double w, h;
    Rectangle(double w, double h) { this.w = w; this.h = h; }
    double area() { return w * h; }
    double perimeter() { return 2 * (w + h); }
    public String toString() { return "Rectangle " + info(); }
  }

  public static void main(String[] args) {
    Shape[] arr = { new Circle(2.0), new Rectangle(3.0, 4.0) };
    for (int i = 0; i < arr.length; i = i + 1) {
      System.out.println(arr[i]);
    }
  }
}