configure gradle

app/build.gradle

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+/*
+ * This file was generated by the Gradle 'init' task.
+ *
+ * This generated file contains a sample Java application project to get you started.
+ * For more details on building Java & JVM projects, please refer to https://docs.gradle.org/9.1.0/userguide/building_java_projects.html in the Gradle documentation.
+ */
+
+plugins {
+    // Apply the application plugin to add support for building a CLI application in Java.
+    id 'application'
+}
+
+repositories {
+    // Use Maven Central for resolving dependencies.
+    mavenCentral()
+}
+
+dependencies {
+    // Use JUnit test framework.
+    testImplementation libs.junit
+
+    // This dependency is used by the application.
+    implementation libs.guava
+}
+
+// Apply a specific Java toolchain to ease working on different environments.
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
+application {
+    // Define the main class for the application.
+    mainClass = 'cn.naipu.App'
+}

app/src/main/java/cn/naipu/App.java

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+/*
+ * This source file was generated by the Gradle 'init' task
+ */
+package app.src.main.java.cn.naipu;
+
+public class App {
+    public String getGreeting() {
+        return "Hello World!";
+    }
+
+    public static void main(String[] args) {
+        System.out.println(new App().getGreeting());
+    }
+}

app/src/test/java/cn/naipu/AppTest.java

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+/*
+ * This source file was generated by the Gradle 'init' task
+ */
+package app.src.test.java.cn.naipu;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+import app.src.main.java.cn.naipu.App;
+
+public class AppTest {
+    @Test public void appHasAGreeting() {
+        App classUnderTest = new App();
+        assertNotNull("app should have a greeting", classUnderTest.getGreeting());
+    }
+}