diff --git a/w4/main.java/Circle.class b/w4/main.java/Circle.class
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diff --git a/w4/main.java/Circle.java b/w4/main.java/Circle.java
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index 0000000..7531856
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+++ b/w4/main.java/Circle.java
@@ -0,0 +1,14 @@
+package w4;
+
+public class Circle extends Shape {
+    private double radius;
+
+    public Circle(double radius) {
+        this.radius = radius;
+    }
+
+    @Override
+    public double getArea() {
+        return Math.PI * radius * radius;
+    }
+}
diff --git a/w4/main.java/Demo.class b/w4/main.java/Demo.class
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diff --git a/w4/main.java/Demo.java b/w4/main.java/Demo.java
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+++ b/w4/main.java/Demo.java
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+package w4.代码;
+
+import w4.Rectangle;
+import w4.Shape;
+import w4.ShapeUtil;
+import w4.Triangle;
+
+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);      // Area: 78.54
+        ShapeUtil.printArea(rectangle);   // Area: 24.00
+        ShapeUtil.printArea(triangle);    // Area: 6.00
+    }
+}
diff --git a/w4/main.java/Rectangle.class b/w4/main.java/Rectangle.class
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