Instructions {#instructions .unnumbered}

• Time allowed: 2 hours

• The test consists of multiple-choice questions, short answer questions, and coding exercises.

• Coding exercises should be implemented in Java. Write clean and optimized code.

• Use appropriate comments to explain your code where necessary.

Core Java (20 points)

Multiple Choice Questions (10 points) {#multiple-choice-questions-10-points .unnumbered}

1. What is the difference between StringBuilder and StringBuffer in Java? (2 points)

   1. StringBuilder is thread-safe, and StringBuffer is not.

   2. StringBuffer is thread-safe, and StringBuilder is not.

   3. Both are immutable.

   4. Both are thread-safe.

2. What does the volatile keyword do in Java? (2 points)

   1. Prevents a variable from being overridden.

   2. Ensures a variable's value is visible to all threads.

   3. Synchronizes a block of code.

   4. Declares a variable as constant.

3. What will the following code print? (2 points)

   int x = 10;
       int y = ++x;
       System.out.println(x + " " + y);

   1. 10 11

   2. 11 10

   3. 11 11

   4. 10 10

4. Which collection allows null keys and values in Java? (2 points)

   1. Hashtable

   2. HashMap

   3. TreeMap

   4. LinkedHashMap

5. Which of the following is not a feature of Java 8? (2 points)

   1. Lambda Expressions

   2. Streams

   3. Modules

   4. Functional Interfaces

Java API Development (30 points)

Short Answer Questions (10 points) {#short-answer-questions-10-points .unnumbered}

1. Explain the purpose of the @RestController annotation in Spring Boot. (5 points)

2. What is the use of the ResponseEntity class in Spring? (5 points)

Coding Challenge (20 points) {#coding-challenge-20-points .unnumbered}

Problem:

• Create a REST API endpoint to manage a list of books. Implement the following:

  1. GET /books: Retrieve all books.

  2. POST /books: Add a new book. Each book should have a unique ID, title, author, and price.

  3. DELETE /books/{id}: Delete a book by ID.

• Write the Java code using Spring Boot.

Database Integration (20 points)

SQL Query (10 points) {#sql-query-10-points .unnumbered}

Write an SQL query to fetch the titles of books that have a price greater than $20 from a table named books.

Coding Challenge (10 points) {#coding-challenge-10-points .unnumbered}

Problem:

• Connect to a MySQL database in Java using JDBC and retrieve all rows from the books table. Display the results in the console.

Debugging and Problem Solving (30 points)

Debugging Task (15 points) {#debugging-task-15-points .unnumbered}

Problem: The following code throws a NullPointerException. Fix the issue.

public class NullPointerExample {
    public static void main(String[] args) {
        String str = null;
        System.out.println(str.length());
    }
}

Problem-Solving Task (15 points) {#problem-solving-task-15-points .unnumbered}

Problem: Write a Java program to find the first non-repeating character in a string.

Scoring Criteria {#scoring-criteria .unnumbered}

• Core Java: 20 points

• API Development: 30 points

• Database Integration: 20 points

• Debugging and Problem Solving: 30 points

Total: 100 points

Please update your code by creating a branch of your name and upload the test file there. The structure of assignment files is totally optional.