添加w4作业文件夹

w4/.gitignore

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+### IntelliJ IDEA ###
+out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+.kotlin
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+bin/
+!**/src/main/**/bin/
+!**/src/test/**/bin/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store

w4/.idea/.gitignore

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+# 默认忽略的文件
+/shelf/
+/workspace.xml
+# 已忽略包含查询文件的默认文件夹
+/queries/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml
+# 基于编辑器的 HTTP 客户端请求
+/httpRequests/

w4/.idea/misc.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_21" default="true" project-jdk-name="21" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/out" />
+  </component>
+</project>

w4/.idea/modules.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/W4.iml" filepath="$PROJECT_DIR$/W4.iml" />
+    </modules>
+  </component>
+</project>

w4/.idea/vcs.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$/.." vcs="Git" />
+  </component>
+</project>

w4/W4.iml

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+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>

w4/src/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;
+    }
+}

w4/src/Main.java

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+public class Main {
+    public static void main(String[] args) {
+        Shape circle = new Circle(2);
+        Shape rectangle = new Rectangle(3, 4);
+        Shape triangle = new Triangle(3, 4);
+
+        ShapeUtil.printArea(circle);
+        ShapeUtil.printArea(rectangle);
+        ShapeUtil.printArea(triangle);
+    }
+}

w4/src/Rectangle.java

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+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;
+    }
+}

w4/src/Shape.java

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

w4/src/ShapeUtil.java

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+public class ShapeUtil {
+    public static void printArea(Shape shape) {
+        if (shape != null) {
+            System.out.println("面积：" + shape.getArea());
+        }
+    }
+}

w4/src/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;
+    }
+}