Room.java

public interface Room {
    double area();
}

public class RectangularRoom implements Room {
    private final double width;
    private final double length;

    public RectangularRoom(double width, double length) {
        this.width = width;
        this.length = length;
    }

    @Override
    public double area() {
        return width * length;
    }
}

public class CircularRoom implements Room {

    private final double radius;

    public CircularRoom(double radius) {
        this.radius = radius;
    }

    @Override
    public double area() {
        return PI * Math.pow(radius, 2);
    }
}