public class Main {
    public static void main(String[] args) {
        // 1. 创建不同图形对象（多态：父类引用指向子类对象）
        Shape circle = new Circle(2);
        Shape rectangle = new Rectangle(3, 4);
        Shape triangle = new Triangle(5, 4);

        // 2. 统一打印面积
        System.out.println("=== 圆的面积 ===");
        ShapeUtil.printArea(circle);

        System.out.println("=== 矩形的面积 ===");
        ShapeUtil.printArea(rectangle);

        System.out.println("=== 三角形的面积 ===");
        ShapeUtil.printArea(triangle);
    }
}