W4  图形面积计算器重构
public abstract class Shape {
    public abstract double getArea();
}
// 圆形类，继承自 Shape
class Circle extends Shape {
    private double radius;
    public Circle(double radius) {
        this.radius = radius;
    }    
    @Override
    public double getArea() {
        return Math.PI * radius * radius;
    }
}
// 矩形类，继承自 Shape
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;
    }
}
// 三角形类，继承自 Shape
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;
    }
}
// 图形工具类，提供统一处理图形的方法
class ShapeUtil {
    // 打印图形面积的方法，接受任意 Shape 子类对象
    public static void printArea(Shape shape) {
        System.out.println("图形面积: " + shape.getArea());
    }
    public static void main(String[] args) {
        // 创建各种图形对象
        Shape circle = new Circle(5.0);
        Shape rectangle = new Rectangle(4.0, 6.0);
        Shape triangle = new Triangle(3.0, 4.0);
        // 统一打印各图形面积
        System.out.println("圆形:");
        printArea(circle);    
        System.out.println("矩形:");
        printArea(rectangle);      
        System.out.println("三角形:");
        printArea(triangle);
    }
}