上传文件至 'w5'

w5/Main.java

@@ -0,0 +1,11 @@
+public class Main {
+    public static void main(String[] args) {
+        Shape circle = new Circle(5);
+        Shape rect = new Rectangle(4, 6);
+        Shape tri = new Triangle(3, 8);
+
+        ShapeUtil.printArea(circle);  // 面积为：78.54
+        ShapeUtil.printArea(rect);    // 面积为：24.00
+        ShapeUtil.printArea(tri);     // 面积为：12.00
+    }
+}

w5/Rectangle.java

@@ -0,0 +1,14 @@
+public 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;
+    }
+}

w5/Shape.java

@@ -0,0 +1,4 @@
+public abstract class Shape {
+    // 抽象方法：没有方法体，强制子类必须实现
+    public abstract double getArea();
+}

w5/ShapeUtil.java

@@ -0,0 +1,6 @@
+public class ShapeUtil {
+    // 参数类型是Shape，传Circle/Rectangle/Triangle都可以 → 这就是多态！
+    public static void printArea(Shape shape) {
+        System.out.printf("面积为：%.2f%n", shape.getArea());
+    }
+}

w5/Triangle.java

@@ -0,0 +1,14 @@
+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;
+    }
+}