diff --git a/w4/Circle.class b/w4/Circle.class
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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/Rectangle.class b/w4/Rectangle.class
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diff --git a/w4/Rectangle.java b/w4/Rectangle.java
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index 0000000..5674664
--- /dev/null
+++ b/w4/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;
+    }
+}
diff --git a/w4/Shape.class b/w4/Shape.class
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diff --git a/w4/Shape.java b/w4/Shape.java
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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.class b/w4/ShapeUtil.class
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diff --git a/w4/ShapeUtil.java b/w4/ShapeUtil.java
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index 0000000..51884ac
--- /dev/null
+++ b/w4/ShapeUtil.java
@@ -0,0 +1,15 @@
+public class ShapeUtil {
+    public static void printArea(Shape shape) {
+        System.out.println("图形面积为：" + shape.getArea());
+    }
+
+    public static void main(String[] args) {
+        Shape circle = new Circle(5);
+        Shape rectangle = new Rectangle(4, 6);
+        Shape triangle = new Triangle(3, 8);
+
+        printArea(circle);
+        printArea(rectangle);
+        printArea(triangle);
+    }
+}
diff --git a/w4/Triangle.class b/w4/Triangle.class
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diff --git a/w4/Triangle.java b/w4/Triangle.java
new file mode 100644
index 0000000..d81b1c5
--- /dev/null
+++ b/w4/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;
+    }
+}
diff --git a/w4/实验报告.txt b/w4/实验报告.txt
new file mode 100644
index 0000000..0a7a8bf
--- /dev/null
+++ b/w4/实验报告.txt
@@ -0,0 +1,13 @@
+“组合 vs 继承”问题解析
+ 
+维度 继承 (Inheritance) 组合 (Composition) 
+定义 子类“是一种”父类（is-a 关系），复用父类代码 类中包含其他类的对象（has-a 关系），复用对象功能 
+耦合度 高，子类与父类强绑定，父类修改会影响所有子类 低，仅依赖对象的接口，修改不影响调用方 
+灵活性 差，继承关系在编译期确定，无法动态修改 好，可在运行时替换组合的对象，适配不同场景 
+适用场景 类之间有明确的层级关系，且父类接口稳定 仅需复用功能，无需共享接口，或需要动态切换实现 
+本实验中的选择 使用继承，因为 Circle/Rectangle/Triangle 本质上“是一种” Shape，且需要统一的  getArea()  接口实现多态 不适合本场景，若用组合则无法实现统一的多态处理
+
+
+1. AI 使用情况：使用 AI 辅助梳理了抽象类与多态的实现逻辑，快速完成了基础代码框架和类图设计，并辅助理解了组合与继承的核心区别。
+2. 核心收获：通过重构，实现了图形的统一处理，新增图形时只需继承  Shape  类，无需修改  ShapeUtil  代码，符合开闭原则。
+3. 反思：继承适合有层级关系的场景，但过度继承会导致类爆炸；组合更灵活，但需要额外的接口抽象，实际开发中应优先考虑组合，必要时结合继承。
diff --git a/w4/类图.txt b/w4/类图.txt
new file mode 100644
index 0000000..9986eb6
--- /dev/null
+++ b/w4/类图.txt
@@ -0,0 +1,22 @@
+类图说明
+ 
+plaintext
+  
+┌─────────────┐
+│    Shape    │  (抽象类)
+├─────────────┤
+│+getArea():double│
+└──────┬──────┘
+                 │
+ ┌─────┴─────┬──────────┐
+ │           │               │
+┌────────┐┌────────────┐┌────────────┐
+│ Circle ││ Rectangle  ││  Triangle  │
+├────────┤├────────────┤├────────────┤
+│-radius ││-width,-height││-base,-height│
+├────────┤├────────────┤├────────────┤
+│getArea()││ getArea() ││ getArea() │
+└────────┘└────────────┘└────────────┘
+ 
+ 
+- 核心关系： Shape  是抽象父类， Circle 、 Rectangle 、 Triangle  继承自  Shape ，实现  getArea()  方法； ShapeUtil  依赖  Shape  类实现统一处理。
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