public class Square implements Shape {
    private Point topLeft;
    private double side;
    public double area() {
        return side*side;
    }
}
public class Rectangle implements Shape {
    private Point topLeft;
    private double height;
    private double width;
    public double area() {
        return height * width;
    }
}
public class Circle implements Shape {
    private Point center;
    private double radius;
    public final double PI = 3.141592653589793;
    public double area() {
        return PI * radius * radius;
    }
}