diff --git a/w4/Circle.java b/w4/Circle.java
new file mode 100644
index 0000000..b3a64bc
--- /dev/null
+++ b/w4/Circle.java
@@ -0,0 +1,12 @@
+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 b/w4/Main.java
new file mode 100644
index 0000000..65461fa
--- /dev/null
+++ b/w4/Main.java
@@ -0,0 +1,11 @@
+public class Main {
+    public static void main(String[] args) {
+        Shape circle = new Circle(5);
+        Shape rectangle = new Rectangle(4, 6);
+        Shape triangle = new Triangle(3, 4, 5);
+
+        ShapeUtil.printArea(circle);
+        ShapeUtil.printArea(rectangle);
+        ShapeUtil.printArea(triangle);
+    }
+}
diff --git a/w4/Rectangle.java b/w4/Rectangle.java
new file mode 100644
index 0000000..6cd9205
--- /dev/null
+++ b/w4/Rectangle.java
@@ -0,0 +1,13 @@
+public class Rectangle extends Shape {
+    private double width, height;
+
+    public Rectangle(double width, double height) {
+        this.width = width;
+        this.height = height;
+    }
+
+    @Override
+    public double getArea() {
+        return width * height;
+    }
+}
diff --git a/w4/Shape.java b/w4/Shape.java
new file mode 100644
index 0000000..ac3b8fb
--- /dev/null
+++ b/w4/Shape.java
@@ -0,0 +1,3 @@
+public abstract class Shape {
+    public abstract double getArea();
+}
diff --git a/w4/ShapeUtil.java b/w4/ShapeUtil.java
new file mode 100644
index 0000000..a5e9fac
--- /dev/null
+++ b/w4/ShapeUtil.java
@@ -0,0 +1,5 @@
+public class ShapeUtil {
+    public static void printArea(Shape shape) {
+        System.out.println("面积为: " + shape.getArea());
+    }
+}
\ No newline at end of file
diff --git a/w4/Triangle.java b/w4/Triangle.java
new file mode 100644
index 0000000..c1311c4
--- /dev/null
+++ b/w4/Triangle.java
@@ -0,0 +1,15 @@
+public class Triangle extends Shape {
+    private double a, b, c;
+
+    public Triangle(double a, double b, double c) {
+        this.a = a;
+        this.b = b;
+        this.c = c;
+    }
+
+    @Override
+    public double getArea() {
+        double s = (a + b + c) / 2;
+        return Math.sqrt(s * (s - a) * (s - b) * (s - c));
+    }
+}