Figures-oriented-task

public abstract class Figure {
    double r1;
    double dx0 = 0.0;   //x_center
    double dy0 = 0.0;   //y_center

    Figure (double a) { r1 = a; }

    abstract double area();
    abstract String name();

    void move (double dx, double dy) {
        dx0 += dx;
        dy0 += dy;
    }
}

class Square extends Figure {

    Square (double a) { super(a); }

    double area() { return Math.pow(r1,2); }

//  public String toString() does the same
    String name() { return "Это квадрат со стороной " + r1; }
}

class Rectangle extends Square {

    double r2;
    Rectangle (double a, double b) {
        super(a);
        r2 = b;
    }

    double area() { return r1*r2; }

    String name() { return "Это четырехугольник со сторонами " + r1 + "," + r2; }
}

class Circle extends Figure {
    Circle (double a) { super(a); } //radius

    double area() { return Math.PI*r1*r1; }

    String name() { return "Это круг радиусом " + r1;    }
}