import java.util.Arrays;

// ========== 1. 抽象类 Shape ==========
abstract class Shape {
    protected String name;
    
    public Shape(String name) {
        this.name = name;
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    public abstract double getArea();
    
    @Override
    public String toString() {
        return name + " - 面积: " + String.format("%.2f", getArea());
    }
}

// ========== 2. 圆形类 ==========
class Circle extends Shape {
    private double radius;
    
    public Circle(String name, double radius) {
        super(name);
        this.radius = radius;
    }
    
    public double getRadius() {
        return radius;
    }
    
    public void setRadius(double radius) {
        this.radius = radius;
    }
    
    @Override
    public double getArea() {
        return Math.PI * radius * radius;
    }
}

// ========== 3. 长方形类 ==========
class Rectangle extends Shape {
    private double length;
    private double width;
    
    public Rectangle(String name, double length, double width) {
        super(name);
        this.length = length;
        this.width = width;
    }
    
    public double getLength() {
        return length;
    }
    
    public void setLength(double length) {
        this.length = length;
    }
    
    public double getWidth() {
        return width;
    }
    
    public void setWidth(double width) {
        this.width = width;
    }
    
    @Override
    public double getArea() {
        return length * width;
    }
}

// ========== 4. 三角形类 ==========
class Triangle extends Shape {
    private double base;
    private double height;
    
    public Triangle(String name, double base, double height) {
        super(name);
        this.base = base;
        this.height = height;
    }
    
    public double getBase() {
        return base;
    }
    
    public void setBase(double base) {
        this.base = base;
    }
    
    public double getHeight() {
        return height;
    }
    
    public void setHeight(double height) {
        this.height = height;
    }
    
    @Override
    public double getArea() {
        return (base * height) / 2;
    }
}

// ========== 5. 工具类 ==========
class ShapeUtil {
    
    public static void printArea(Shape shape) {
        if (shape == null) {
            System.out.println("形状不能为空");
            return;
        }
        System.out.println(shape.toString());
    }
    
    public static void printAreas(Shape[] shapes) {
        System.out.println("=== 形状面积列表 ===");
        for (Shape shape : shapes) {
            printArea(shape);
        }
        System.out.println("==================");
    }
}

// ========== 6. 主类（必须是public，且与文件名相同）==========
public class Main {
    public static void main(String[] args) {
        // 创建各种形状
        Circle circle = new Circle("圆形", 5.0);
        Rectangle rectangle = new Rectangle("长方形", 4.0, 6.0);
        Triangle triangle = new Triangle("三角形", 3.0, 4.0);
        
        // 使用工具类打印面积
        System.out.println("单个形状面积打印：");
        ShapeUtil.printArea(circle);
        ShapeUtil.printArea(rectangle);
        ShapeUtil.printArea(triangle);
        
        // 多态演示：批量处理
        System.out.println("\n批量处理（多态演示）：");
        Shape[] shapes = {circle, rectangle, triangle};
        ShapeUtil.printAreas(shapes);
    }
}