ADT in Java

Shapes.java

public sealed interface Shape permits Shape.Rectangle, Shape.Square, Shape.Circle {
    record Circle(double radius) implements Shape {}
    record Rectangle(double length, double width) implements Shape {}
    record Square(double side) implements Shape {}
}

public class Main {

    public static double calculateArea(Shape shape) {
        return switch (shape) {
            case Shape.Circle(var radius) -> Math.PI * Math.pow(radius, 2);
            case Shape.Rectangle(var length, var width) -> length * width;
            case Shape.Square(var side) -> Math.pow(side, 2);
        };
    }
  
    public static void main(String[] args) {
        var circle = new Shape.Circle(5.0);
        var rectangle = new Shape.Rectangle(4.0, 6.0);
        var square = new Shape.Square(3.0);

        System.out.println("Circle area: " + calculateArea(circle));
        System.out.println("Rectangle area: " + calculateArea(rectangle));
        System.out.println("Square area: " + calculateArea(square));
    }  
}