diff --git a/w4/Circle.java b/w4/Circle.java
new file mode 100644
index 0000000..e175c22
--- /dev/null
+++ b/w4/Circle.java
@@ -0,0 +1,27 @@
+package com.shape;
+
+public class Circle extends Shape {
+    private double radius;   // 半径
+
+    public Circle(double radius) {
+        if (radius <= 0) {
+            throw new IllegalArgumentException("半径必须大于0");
+        }
+        this.radius = radius;
+    }
+
+    public double getRadius() {
+        return radius;
+    }
+
+    public void setRadius(double radius) {
+        if (radius > 0) {
+            this.radius = radius;
+        }
+    }
+
+    @Override
+    public double getArea() {
+        return Math.PI * radius * radius;   // πr²
+    }
+}
\ No newline at end of file
diff --git a/w4/Rectangle.java b/w4/Rectangle.java
new file mode 100644
index 0000000..070bfa4
--- /dev/null
+++ b/w4/Rectangle.java
@@ -0,0 +1,35 @@
+package com.shape;
+
+public class Rectangle extends Shape {
+    private double width;    // 宽度
+    private double height;   // 高度
+
+    public Rectangle(double width, double height) {
+        if (width <= 0 || height <= 0) {
+            throw new IllegalArgumentException("长和宽必须大于0");
+        }
+        this.width = width;
+        this.height = height;
+    }
+
+    public double getWidth() {
+        return width;
+    }
+
+    public void setWidth(double width) {
+        if (width > 0) this.width = width;
+    }
+
+    public double getHeight() {
+        return height;
+    }
+
+    public void setHeight(double height) {
+        if (height > 0) this.height = height;
+    }
+
+    @Override
+    public double getArea() {
+        return width * height;   // 长 × 宽
+    }
+}
\ No newline at end of file
diff --git a/w4/Shape.java b/w4/Shape.java
new file mode 100644
index 0000000..7fc4019
--- /dev/null
+++ b/w4/Shape.java
@@ -0,0 +1,22 @@
+package com.shape;
+
+/**
+ * 抽象类 Shape
+ * 提供统一的面积计算接口
+ */
+public abstract class Shape {
+
+    /**
+     * 抽象方法：计算图形面积
+     * 子类必须实现该方法
+     * @return 图形的面积（double类型）
+     */
+    public abstract double getArea();
+
+    /**
+     * 通用方法：打印图形信息（可选，方便扩展）
+     */
+    public void display() {
+        System.out.println(this.getClass().getSimpleName() + " 的面积为: " + getArea());
+    }
+}
\ No newline at end of file
diff --git a/w4/ShapeUtil.java b/w4/ShapeUtil.java
new file mode 100644
index 0000000..b82cd55
--- /dev/null
+++ b/w4/ShapeUtil.java
@@ -0,0 +1,23 @@
+package com.shape;
+
+/**
+ * Shape 工具类
+ * 利用多态统一处理不同图形
+ */
+public class ShapeUtil {
+
+    /**
+     * 打印任意 Shape 子类的面积
+     * 体现了多态：同一个方法可以接收不同子类对象
+     * @param shape 任意继承自 Shape 的图形对象
+     */
+    public static void printArea(Shape shape) {
+        if (shape == null) {
+            System.out.println("图形对象不能为空！");
+            return;
+        }
+        System.out.printf("%s 的面积是: %.4f%n",
+                shape.getClass().getSimpleName(),
+                shape.getArea());
+    }
+}
\ No newline at end of file
diff --git a/w4/TestShape.java b/w4/TestShape.java
new file mode 100644
index 0000000..f59aee6
--- /dev/null
+++ b/w4/TestShape.java
@@ -0,0 +1,29 @@
+package com.shape;
+
+public class TestShape {
+    public static void main(String[] args) {
+        System.out.println("=== 图形面积计算器（使用抽象类重构）===\n");
+
+        // 创建不同图形对象
+        Circle circle = new Circle(5.0);
+        Rectangle rectangle = new Rectangle(4.0, 6.0);
+        Triangle triangle = new Triangle(3.0, 4.0, 5.0);
+
+        // 使用 ShapeUtil 统一处理（多态体现）
+        ShapeUtil.printArea(circle);
+        ShapeUtil.printArea(rectangle);
+        ShapeUtil.printArea(triangle);
+
+        System.out.println("\n=== 使用 display() 方法 ===");
+        circle.display();
+        rectangle.display();
+        triangle.display();
+
+        // 多态数组示例（进一步展示统一处理优势）
+        System.out.println("\n=== 多态数组演示 ===");
+        Shape[] shapes = {circle, rectangle, triangle};
+        for (Shape s : shapes) {
+            ShapeUtil.printArea(s);
+        }
+    }
+}
\ No newline at end of file