abstract class Shape {
    public abstract double getArea();
}

class Circle extends Shape {
    private double radius;

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

    @Override
    public double getArea() {
        return Math.PI * radius * radius;
    }
}

class Rectangle extends Shape {
    private double width;
    private double height;

    public Rectangle(double width, double height) {
        this.width = width;
        this.height = height;
    }

    @Override
    public double getArea() {
        return width * height;
    }
}

class Triangle extends Shape {
    private double base;
    private double height;

    public Triangle(double base, double height) {
        this.base = base;
        this.height = height;
    }

    @Override
    public double getArea() {
        return 0.5 * base * height;
    }
}

class ShapeUtil {
    public static void printArea(Shape shape) {
        double area = shape.getArea();
        System.out.println("该图形的面积是: " + area);
    }
}

public class AreaCalculator {
    public static void main(String[] args) {
        Shape circle = new Circle(5.0);
        Shape rectangle = new Rectangle(4.0, 6.0);
        Shape triangle = new Triangle(3.0, 8.0);

        System.out.println("--- 图形面积计算 ---");
        ShapeUtil.printArea(circle);
        ShapeUtil.printArea(rectangle);
        ShapeUtil.printArea(triangle);
    }
}