上传文件至 'w4'

w4/Circle.java

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+public class Circle extends Shape {
+    private double radius;
+
+    public Circle(double radius) {
+        this.radius = radius;
+    }
+
+    public double getRadius() { return radius; }
+
+    @Override
+    public double getArea() {
+        return Math.PI * radius * radius;
+    }
+}

w4/Main.java

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+public class Main {
+    public static void main(String[] args) {
+        // 创建图形对象
+        Shape circle    = new Circle(5.0);
+        Shape rectangle = new Rectangle(4.0, 6.0);
+        Shape triangle  = new Triangle(3.0, 8.0);
+
+        // 存入数组，统一处理（多态）
+        Shape[] shapes = { circle, rectangle, triangle };
+
+        System.out.println("===== 图形面积计算器 =====");
+        for (Shape s : shapes) {
+            ShapeUtil.printArea(s);
+        }
+
+        System.out.println();
+        Shape largest = ShapeUtil.findLargest(shapes);
+        System.out.println("面积最大的图形是：" + largest.getName()
+                           + "（面积 = " + String.format("%.2f", largest.getArea()) + "）");
+    }
+}

w4/Rectangle.java

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+public class Rectangle extends Shape {
+    private double width;
+    private double height;
+
+    public Rectangle(double width, double height) {
+        this.width = width;
+        this.height = height;
+    }
+
+    public double getWidth()  { return width; }
+    public double getHeight() { return height; }
+
+    @Override
+    public double getArea() {
+        return width * height;
+    }
+}

w4/Shape.java

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+public abstract class Shape {
+    // 抽象方法：计算面积，子类必须实现
+    public abstract double getArea();
+
+    // 通用方法：返回图形名称（子类可重写）
+    public String getName() {
+        return this.getClass().getSimpleName();
+    }
+}

w4/ShapeUtil.java

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+public class ShapeUtil {
+    /**
+     * 统一打印任意图形的面积（多态调用）
+     */
+    public static void printArea(Shape shape) {
+        System.out.printf("%s 的面积为：%.2f%n", shape.getName(), shape.getArea());
+    }
+
+    /**
+     * 找出面积最大的图形
+     */
+    public static Shape findLargest(Shape[] shapes) {
+        Shape largest = shapes[0];
+        for (Shape s : shapes) {
+            if (s.getArea() > largest.getArea()) {
+                largest = s;
+            }
+        }
+        return largest;
+    }
+}