feat:W3

W3/Circle.java

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+public class Circle extends Shape {
+    private double radius;
+
+    public Circle(double radius) {
+        this.radius = radius;
+    }
+
+    @Override
+    public double getArea() {
+        return Math.PI * radius * radius;
+    }
+}

W3/Rectangle.java

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+public class Rectangle extends Shape {
+    private double length;
+    private double width;
+
+    public Rectangle(double length, double width) {
+        this.length = length;
+        this.width = width;
+    }
+
+    @Override
+    public double getArea() {
+        return length * width;
+    }
+}

W3/Shape.java

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+public abstract class Shape {
+    public abstract double getArea();
+}

W3/ShapeClassDiagram.md

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+# 形状类图
+
+```
++-------------------+
+|     Shape         |
++-------------------+
+| +getArea():double |
++-------------------+
+         ^
+         | 继承
++---------+----------+
+|                    |
+v                    v
++----------------+   +-------------------+   +----------------+
+|    Circle      |   |    Rectangle      |   |    Triangle    |
++----------------+   +-------------------+   +----------------+
+| -radius:double |   | -length:double    |   | -base:double   |
+|                |   | -width:double     |   | -height:double |
++----------------+   +-------------------+   +----------------+
+| +getArea():double | | +getArea():double | | +getArea():double |
++----------------+   +-------------------+   +----------------+
+
++-------------------+
+|    ShapeUtil      |
++-------------------+
+| +printArea(Shape):void |
+| +main(String[]):void   |
++-------------------+
+```
+
+## 类说明
+
+1. **Shape** - 抽象类，定义了计算面积的抽象方法
+2. **Circle** - 圆形，继承自 Shape，使用 π×r² 计算面积
+3. **Rectangle** - 矩形，继承自 Shape，使用长×宽计算面积
+4. **Triangle** - 三角形，继承自 Shape，使用 0.5×底×高计算面积
+5. **ShapeUtil** - 工具类，用于测试不同形状的面积计算
+
+## 多态特性
+
+ShapeUtil.printArea() 方法接收 Shape 类型参数，但运行时会根据实际传入的子类对象调用对应的 getArea() 方法，体现了 Java 的多态特性。

W3/ShapeUtil.java

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+public class ShapeUtil {
+
+    public void printArea(Shape shape) {
+        System.out.println("图形的面积为：" + shape.getArea());
+    }
+
+    public static void main(String[] args) {
+        ShapeUtil util = new ShapeUtil();
+        util.printArea(new Circle(5));
+        util.printArea(new Rectangle(4, 3));
+        util.printArea(new Triangle(3, 4));
+    }
+}

W3/Triangle.java

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+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;
+    }
+}

W3/实验报告.txt

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+通过AI先编写了完整程序，并要求AI一步步讲解代码。随后自行操作，通过AI查找错误点，并运用AI绘制类图并讲解意义。
+继承：子类和父辈强绑定
+组合：类之间依赖松散