添加 'w4/Main.java'

w4/Main.java

@@ -0,0 +1,70 @@
+// Shape.java
+public abstract class Shape {
+    public abstract double getArea();
+}
+
+// Circle.java
+public class Circle extends Shape {
+    private double radius;
+
+    public Circle(double radius) {
+        this.radius = radius;
+    }
+
+    @Override
+    public double getArea() {
+        return Math.PI * radius * radius;
+    }
+}
+
+// Rectangle.java
+public class Rectangle extends Shape {
+    private double length;
+    private double width;
+
+    public Rectangle(double length, double width) {
+        this.length = length;
+        this.width = width;
+    }
+
+    @Override
+    public double getArea() {
+        return length * width;
+    }
+}
+
+// Triangle.java
+public 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;
+    }
+}
+
+// ShapeUtil.java
+public class ShapeUtil {
+    public static void printArea(Shape shape) {
+        System.out.printf("图形面积：%.2f\n", shape.getArea());
+    }
+}
+
+// Demo.java（测试类，展示多态）
+public class Demo {
+    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, 4.0);
+
+        ShapeUtil.printArea(circle);      // 图形面积：78.54
+        ShapeUtil.printArea(rectangle);   // 图形面积：24.00
+        ShapeUtil.printArea(triangle);    // 图形面积：6.00
+    }
+}