Finished the code might add some changes

.gitignore

+target/

pom.xml

+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>com.quiz</groupId>
+  <artifactId>QuizRMI</artifactId>
+  <packaging>jar</packaging>
+  <version>1.0-SNAPSHOT</version>
+  <name>QuizRMI</name>
+  <url>http://maven.apache.org</url>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>3.8.1</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+<build>
+    <plugins>
+        <plugin>
+            <groupId>org.apache.maven.plugins</groupId>
+            <artifactId>maven-compiler-plugin</artifactId>
+            <version>3.10.1</version>
+            <configuration>
+                <source>17</source> <!-- or 11, or 8 -->
+                <target>17</target> <!-- same as source -->
+            </configuration>
+        </plugin>
+    </plugins>
+</build>
+
+</project>

src/main/java/com/quiz/client/QuizClient.java

+package com.quiz.client;
+import com.quiz.common.*;
+import java.rmi.registry.LocateRegistry;
+import java.rmi.registry.Registry;
+import java.rmi.server.UnicastRemoteObject;
+import java.util.Scanner;
+
+public class QuizClient extends UnicastRemoteObject implements QuizCallback {
+
+    private QuizService service;
+    private String studentName;
+
+    protected QuizClient(String name) throws Exception {
+        super();
+        this.studentName = name;
+        Registry registry = LocateRegistry.getRegistry("localhost", 1099);
+        service = (QuizService) registry.lookup("QuizService");
+        service.registerCallback(studentName, this);
+    }
+
+    @Override
+    public void updateLeaderboard(String leaderboard) {
+        System.out.println("\n--- Leaderboard Update ---\n" + leaderboard);
+    }
+
+    public void start() throws Exception {
+        Scanner sc = new Scanner(System.in);
+        while (true) {
+            Question q = service.getQuestion(studentName);
+            System.out.println("Question: " + q.getQuestion());
+            System.out.print("Your Answer: ");
+            String ans = sc.nextLine();
+            String feedback = service.submitAnswer(studentName, ans);
+            System.out.println(feedback);
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        Scanner sc = new Scanner(System.in);
+        System.out.print("Enter your name: ");
+        String name = sc.nextLine();
+        QuizClient client = new QuizClient(name);
+        client.start();
+    }
+}

src/main/java/com/quiz/common/Question.java

+package com.quiz.common;
+import java.io.Serializable;
+
+public class Question implements Serializable {
+    private String question;
+    private String answer;
+
+    public Question(String question, String answer) {
+        this.question = question;
+        this.answer = answer;
+    }
+
+    public String getQuestion() { return question; }
+    public String getAnswer() { return answer; }
+}

src/main/java/com/quiz/common/QuizCallback.java

+package com.quiz.common;
+import java.rmi.Remote;
+import java.rmi.RemoteException;
+
+public interface QuizCallback extends Remote {
+    void updateLeaderboard(String leaderboard) throws RemoteException;
+}

src/main/java/com/quiz/common/QuizService.java

+package com.quiz.common;
+import java.rmi.Remote;
+import java.rmi.RemoteException;
+
+public interface QuizService extends Remote {
+    Question getQuestion(String studentName) throws RemoteException;
+    String submitAnswer(String studentName, String answer) throws RemoteException;
+    void registerCallback(String studentName, QuizCallback callback) throws RemoteException;
+}

src/main/java/com/quiz/common/StudentScore.java

+package com.quiz.common;
+import java.io.Serializable;
+
+public class StudentScore implements Serializable {
+    private String name;
+    private int score;
+
+    public StudentScore(String name) {
+        this.name = name;
+        this.score = 0;
+    }
+
+    public String getName() { return name; }
+    public int getScore() { return score; }
+    public void incrementScore() { score++; }
+}

src/main/java/com/quiz/server/QuizServer.java

+package com.quiz.server;
+import com.quiz.common.*;
+import java.rmi.RemoteException;
+import java.rmi.server.UnicastRemoteObject;
+import java.rmi.registry.LocateRegistry;
+import java.rmi.registry.Registry;
+import java.util.*;
+
+public class QuizServer extends UnicastRemoteObject implements QuizService {
+
+    private Map<String, StudentScore> studentScores = new HashMap<>();
+    private List<Question> questions = new ArrayList<>();
+    private Map<String, Question> currentQuestions = new HashMap<>();
+    private Map<String, QuizCallback> callbacks = new HashMap<>();
+
+    protected QuizServer() throws RemoteException {
+        super();
+        questions.add(new Question("What is 2 + 2?", "4"));
+        questions.add(new Question("Capital of France?", "Paris"));
+        questions.add(new Question("Java is ___?", "Programming language"));
+    }
+
+    @Override
+    public Question getQuestion(String studentName) throws RemoteException {
+        studentScores.putIfAbsent(studentName, new StudentScore(studentName));
+        Question q = questions.get(new Random().nextInt(questions.size()));
+        currentQuestions.put(studentName, q);
+        return q;
+    }
+
+    @Override
+    public String submitAnswer(String studentName, String answer) throws RemoteException {
+        Question q = currentQuestions.get(studentName);
+        if (q == null) return "No question assigned!";
+        String feedback;
+        if (q.getAnswer().equalsIgnoreCase(answer.trim())) {
+            studentScores.get(studentName).incrementScore();
+            feedback = "Correct! Score: " + studentScores.get(studentName).getScore();
+        } else {
+            feedback = "Wrong! Score: " + studentScores.get(studentName).getScore();
+        }
+        updateLeaderboard();
+        return feedback;
+    }
+
+    @Override
+    public void registerCallback(String studentName, QuizCallback callback) throws RemoteException {
+        callbacks.put(studentName, callback);
+    }
+
+    private void updateLeaderboard() {
+        List<StudentScore> top = new ArrayList<>(studentScores.values());
+        top.sort((a, b) -> b.getScore() - a.getScore());
+        StringBuilder leaderboard = new StringBuilder("Leaderboard:\n");
+        for (int i = 0; i < Math.min(3, top.size()); i++) {
+            leaderboard.append((i+1) + ". " + top.get(i).getName() + " - " + top.get(i).getScore() + "\n");
+        }
+        for (QuizCallback cb : callbacks.values()) {
+            try { cb.updateLeaderboard(leaderboard.toString()); }
+            catch (Exception ignored) {}
+        }
+    }
+
+    public static void main(String[] args) {
+        try {
+            QuizServer server = new QuizServer();
+            Registry registry = LocateRegistry.createRegistry(1099);
+            registry.rebind("QuizService", server);
+            System.out.println("Quiz Server is running...");
+synchronized (server) {
+            server.wait();
+        }
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+}

src/test/java/com/quiz/AppTest.java

+package com.quiz;
+
+import junit.framework.Test;
+import junit.framework.TestCase;
+import junit.framework.TestSuite;
+
+/**
+ * Unit test for simple App.
+ */
+public class AppTest 
+    extends TestCase
+{
+    /**
+     * Create the test case
+     *
+     * @param testName name of the test case
+     */
+    public AppTest( String testName )
+    {
+        super( testName );
+    }
+
+    /**
+     * @return the suite of tests being tested
+     */
+    public static Test suite()
+    {
+        return new TestSuite( AppTest.class );
+    }
+
+    /**
+     * Rigourous Test :-)
+     */
+    public void testApp()
+    {
+        assertTrue( true );
+    }
+}