Example Sum Type with Pattern Matching

Shapes.java

import java.util.List;

sealed interface Shape permits Circle, Rectangle, Triangle, Pentagon {}

record Circle(double radius) implements Shape {}
record Rectangle(double width, double height) implements Shape {}
record Triangle(double side1, double side2, double side3) implements Shape {}
record Pentagon(double side) implements Shape {}


class Shapes {

  static double area(Shape shape) {
    return switch (shape) {
      case Circle(double radius) -> Math.PI * radius * radius;
      case Rectangle(double width, double height) -> width * height;
      case Triangle(double side1, double side2, double side3) -> {
        double s = (side1 + side2 + side3) / 2;
        yield Math.sqrt(s * (s - side1) * (s - side2) * (s - side3));
      }
      case Pentagon(double side) -> (0.25) * Math.sqrt(5 * (5 + 2 * Math.sqrt(5))) * side * side;
    };
  }

  static double perimeter(Shape shape) {
    return switch (shape) {
      case Circle(double radius) -> 2 * Math.PI * radius;
      case Rectangle(double width, double height) -> 2 * (width + height);
      case Triangle(double side1, double side2, double side3) -> side1 + side2 + side3;
      case Pentagon(double side) -> 5 * side;
    };
  }

  static String info(Shape shape) {
    return switch (shape) {
      case Circle c ->
          "Circle with radius: %.2f, area: %.2f, perimeter: %.2f".formatted(c.radius(), area(c), perimeter(c));
      case Rectangle r ->
          "Rectangle with width: %.2f , height: %.2f, area: %.2f, perimeter: %.2f".formatted(r.width(), r.height(), area(r), perimeter(r));
      case Triangle t ->
          "Triangle with sides: %.2f, %.2f, %.2f, area: %.2f, perimeter: %.2f".formatted(t.side1(), t.side2(), t.side3(), area(t), perimeter(t));
      case Pentagon p ->
          "Pentagon with side: %.2f, area: %.2f, perimeter: %.2f".formatted(p.side(), area(p), perimeter(p));
    };
  }

  static Shape scale(Shape shape, double scaleFactor) {
    return switch (shape) {
      case Circle c -> new Circle(c.radius() * scaleFactor);
      case Rectangle r -> new Rectangle(r.width() * scaleFactor, r.height() * scaleFactor);
      case Triangle t -> new Triangle(t.side1() * scaleFactor, t.side2() * scaleFactor, t.side3() * scaleFactor);
      case Pentagon p -> new Pentagon(p.side() * scaleFactor);
    };
  }

  public static void main(String[] args) {
    List<Shape> shapes = List.of(new Circle(5), new Triangle(3, 3, 3), new Rectangle(3, 5), new Pentagon(5.6));

    System.out.println("\nShapes: " + shapes);
    shapes.stream().map(Shapes::info).forEach(System.out::println);

    System.out.println("\nShapes : " + shapes + " scaled by 2");
    shapes.stream().map(s -> Shapes.scale(s, 2)).map(Shapes::info).forEach(System.out::println);
  }
}