40 (сравнение двух площадей)

abstract class Shape {
    public int compareTo (Shape s) {
        if (s == null) {
            throw new NullPointerException();
        }
        if (this.getArea() > s.getArea()) {
            return 1;
        }
        if (this.getArea() < s.getArea()) {
            return -1;
        }
        return 0;
    }
    double getArea() {
        return 0;
    }
}

class Circle extends Shape {
    public Circle(double r) {
        this.r = r;
    }

    double r;
    double getArea() {
        return Math.PI*r*r;
        }
}

class Square extends Shape {
    public Square(double a) {
        this.a = a;
    }

    double a;

    double getArea() {
        return a*a;
    }
}

class Rect extends Shape {
    double a;
    double b;
        public Rect(int a, int b) {
            this.a = a;
            this.b = b;
        }
        double getArea() {
            return a*b;
        }
}
public class Main {
    public static double area (double p, double a, double b, double c) {
        return Math.sqrt(p*(p-a)*(p-b)*(p-c));
    }
    Shape s1;
    Shape s2;
    public static void main(String[] args) {

        Shape s1 = new Rect(5,5);
        Shape s2 = new Square(2);
        System.out.println(s1.compareTo(s2));

    }
}