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Merge pull request #18358 from dhrubo55/BAEL-8962-Check-if-a-code-compiles-in-Java-using-JavaCompiler
[BAEL-8962] Check if a code compiles in Java using JavaCompiler
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‎core-java-modules/core-java-compiler/pom.xml

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<artifactId>core</artifactId>
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<version>${gdata.version}</version>
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</dependency>
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<dependency>
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<groupId>org.slf4j</groupId>
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<artifactId>slf4j-api</artifactId>
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<version>${org.slf4j.version}</version>
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</dependency>
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<dependency>
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<groupId>com.github.stefanbirkner</groupId>
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<artifactId>system-lambda</artifactId>
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<version>${system-lambda-version}</version>
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</dependency>
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</dependencies>
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<properties>
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<gdata.version>1.47.1</gdata.version>
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<system-lambda-version>1.2.1</system-lambda-version>
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</properties>
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</project>

‎core-java-modules/core-java-compiler/src/main/java/com/baeldung/compilerapi/InMemoryJavaFile.java

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package com.baeldung.compilerapi;
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import javax.tools.SimpleJavaFileObject;
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import java.net.URI;
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public class InMemoryJavaFile extends SimpleJavaFileObject {
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private final String code;
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InMemoryJavaFile(String name, String code) {
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super(URI.create("string:///" + name.replace('.', '/') + Kind.SOURCE.extension), Kind.SOURCE);
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this.code = code;
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}
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@Override
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public CharSequence getCharContent(boolean ignoreEncodingErrors) {
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return code;
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}
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}

‎core-java-modules/core-java-compiler/src/main/java/com/baeldung/compilerapi/JavaCompilerUtils.java

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package com.baeldung.compilerapi;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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import javax.tools.*;
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import java.io.*;
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import java.net.URL;
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import java.net.URLClassLoader;
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import java.nio.charset.StandardCharsets;
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import java.nio.file.Files;
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import java.nio.file.Path;
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import java.util.*;
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public class JavaCompilerUtils {
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private final JavaCompiler compiler;
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private final StandardJavaFileManager standardFileManager;
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private final Path outputDirectory;
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private static final Logger logger = LoggerFactory.getLogger(JavaCompilerUtils.class);
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public JavaCompilerUtils(Path outputDirectory) throws IOException {
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this.outputDirectory = outputDirectory;
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this.compiler = ToolProvider.getSystemJavaCompiler();
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if (compiler == null) {
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throw new IllegalStateException("Java compiler not available. Ensure you're using JDK, not JRE.");
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}
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this.standardFileManager = compiler.getStandardFileManager(null, null, StandardCharsets.UTF_8);
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if (!Files.exists(outputDirectory)) {
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Files.createDirectories(outputDirectory);
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}
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standardFileManager.setLocation(StandardLocation.CLASS_OUTPUT, Collections.singleton(outputDirectory.toFile()));
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}
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public boolean compileFile(Path sourceFile) {
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if (!Files.exists(sourceFile)) {
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throw new IllegalArgumentException("Source file does not exist: " + sourceFile);
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}
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try {
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Iterable<? extends JavaFileObject> compilationUnits =
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standardFileManager.getJavaFileObjectsFromFiles(Collections.singletonList(sourceFile.toFile()));
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return compile(compilationUnits);
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} catch (Exception e) {
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logger.error("Compilation failed: ", e);
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return false;
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}
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}
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public boolean compileFromString(String className, String sourceCode) {
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JavaFileObject sourceObject = new InMemoryJavaFile(className, sourceCode);
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return compile(Collections.singletonList(sourceObject));
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}
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private boolean compile(Iterable<? extends JavaFileObject> compilationUnits) {
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DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<>();
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JavaCompiler.CompilationTask task = compiler.getTask(
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null,
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standardFileManager,
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diagnostics,
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null,
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null,
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compilationUnits
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);
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boolean success = task.call();
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for (Diagnostic<? extends JavaFileObject> diagnostic : diagnostics.getDiagnostics()) {
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logger.debug(diagnostic.getMessage(null));
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}
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return success;
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}
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public void runClass(String className, String... args) throws Exception {
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try (URLClassLoader classLoader = new URLClassLoader(new URL[]{outputDirectory.toUri().toURL()})) {
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Class<?> loadedClass = classLoader.loadClass(className);
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loadedClass.getMethod("main", String[].class).invoke(null, (Object) args);
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}
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}
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public Path getOutputDirectory() {
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return outputDirectory;
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}
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}

‎core-java-modules/core-java-compiler/src/test/java/com/baeldung/compilerapi/JavaCompilerUnitTest.java

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package com.baeldung.compilerapi;
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import org.junit.jupiter.api.*;
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import org.junit.jupiter.api.io.TempDir;
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import java.nio.file.Files;
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import java.nio.file.Path;
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import java.nio.file.Paths;
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import static com.github.stefanbirkner.systemlambda.SystemLambda.tapSystemErr;
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import static com.github.stefanbirkner.systemlambda.SystemLambda.tapSystemOut;
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import static org.junit.jupiter.api.Assertions.*;
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public class JavaCompilerUnitTest {
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@TempDir
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static Path tempDir;
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private JavaCompilerUtils compilerUtil;
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@BeforeEach
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void setUp() throws Exception {
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Path outputDir = tempDir.resolve("classes");
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Files.createDirectories(outputDir);
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compilerUtil = new JavaCompilerUtils(outputDir);
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}
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@Test
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void givenSimpleHelloWorldClass_whenCompiledFromString_thenCompilationSucceeds() {
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String className = "HelloWorld";
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String sourceCode = "public class HelloWorld {\n" +
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" public static void main(String[] args) {\n" +
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" System.out.println(\"Hello, World!\");\n" +
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" }\n" +
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"}";
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boolean result = compilerUtil.compileFromString(className, sourceCode);
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assertTrue(result, "Compilation should succeed");
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Path classFile = compilerUtil.getOutputDirectory().resolve(className + ".class");
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assertTrue(Files.exists(classFile), "Class file should be created");
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}
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@Test
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void givenClassWithPackage_whenCompiledFromString_thenCompilationSucceedsInPackageDirectory() {
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String className = "com.example.PackagedClass";
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String sourceCode = "package com.example;\n\n" +
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"public class PackagedClass {\n" +
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" public static void main(String[] args) {\n" +
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" System.out.println(\"Hello from packaged class!\");\n" +
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" }\n" +
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"}";
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boolean result = compilerUtil.compileFromString(className, sourceCode);
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assertTrue(result, "Compilation should succeed");
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Path classFile = compilerUtil.getOutputDirectory().resolve(
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Paths.get("com", "example", "PackagedClass.class"));
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assertTrue(Files.exists(classFile), "Class file should be created in the package directory");
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}
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@Test
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void givenClassWithSyntaxError_whenCompiledFromString_thenCompilationFails() {
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String className = "ErrorClass";
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String sourceCode = "public class ErrorClass {\n" +
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" public static void main(String[] args) {\n" +
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" System.out.println(\"This has an error\")\n" +
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" }\n" +
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"}";
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boolean result = compilerUtil.compileFromString(className, sourceCode);
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assertFalse(result, "Compilation should fail due to syntax error");
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Path classFile = compilerUtil.getOutputDirectory().resolve(className + ".class");
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assertFalse(Files.exists(classFile), "No class file should be created for failed compilation");
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}
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@Test
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void givenJavaSourceFile_whenCompiled_thenCompilationSucceeds() throws Exception {
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String className = "FileTest";
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String sourceCode = "public class FileTest {\n" +
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" public static void main(String[] args) {\n" +
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" System.out.println(\"Hello from file!\");\n" +
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" }\n" +
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"}";
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Path sourceFile = tempDir.resolve(className + ".java");
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Files.write(sourceFile, sourceCode.getBytes());
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boolean result = compilerUtil.compileFile(sourceFile);
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assertTrue(result, "Compilation should succeed");
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Path classFile = compilerUtil.getOutputDirectory().resolve(className + ".class");
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assertTrue(Files.exists(classFile), "Class file should be created");
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}
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@Test
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void givenCompiledClass_whenRunWithArguments_thenOutputsExpectedResult() throws Exception {
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String className = "Runner";
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String sourceCode = "public class Runner {\n" +
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" public static void main(String[] args) {\n" +
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" System.out.println(\"Running: \" + String.join(\", \", args));\n" +
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" }\n" +
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"}";
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boolean result = compilerUtil.compileFromString(className, sourceCode);
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assertTrue(result, "Compilation should succeed");
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String output = tapSystemOut(() -> {
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compilerUtil.runClass(className, "arg1", "arg2");
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});
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assertEquals("Running: arg1, arg2", output.trim());
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}
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@Test
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void whenCompilingNonExistentFile_thenThrowsIllegalArgumentException() {
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Path nonExistentFile = tempDir.resolve("NonExistent.java");
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assertThrows(IllegalArgumentException.class, () -> {
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compilerUtil.compileFile(nonExistentFile);
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});
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}
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}

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