Luxoft 

Luxoft Interview Questions:

1. Multithreading:

   • What is the difference between submit() and execute() in the ExecutorService?

   • Explain the lifecycle of threads.

   • What is volatile used for in Java?

   • How is a deadlock generated? (Hint: Synchronized methods, code, and block)

2. Exceptions and Errors:

   • What is the difference between Exceptions and Errors?

   • How do you customize unchecked exceptions?

3. HashMap and Collections:

   • Explain how HashMap works and discuss its time complexity.

   • What are some common problems with HashMap keys, especially when the key is an object that changes its value?

   • What is the difference between HashTable and ConcurrentMap?

   • Explain TreeSet vs HashSet.

   • How do you implement Comparable and Comparator?

4. User Class Coding Exercise:

   • Create a User class with three attributes.

   • Create six users (four females, two males).

   • Calculate the average age of all females.

5. Interface Modifications:

   • Create an interface with four methods: a(), b(), c(), and d().

   • Change the interface so that method b() is a default method, and method c() is a private static method.

   • Can you call a method from this interface using lambda expressions? If not, how would you modify the interface to make it possible?

6. Java Stack and Application Architecture:

   • Explain the Java memory model: heap vs. stack.

   • What is the string pool?

   • What is the difference between POST and PUT in REST?

   • What are the core differences between Service and Repository annotations in Spring?

7. Design Patterns and SOLID Principles:

   • Explain common design patterns like Adapter, Decorator, and Observer.

   • Discuss SOLID principles. Which principle is your favorite, and why?

   • How do you implement immutable objects in Java?

8. Spring and Microservices:

   • What annotations do you use for Spring transactions and database handling? What is the best way to inject dependencies (constructor, variable, or setter)?

   • Explain Spring Boot, microservices architecture, and real-time problem solving.

   • What is the difference between @ControllerAdvice, @Conditional, and @Profile annotations?

   • How do you handle exceptions in Spring controllers?

9. Concurrency and Performance:

   • Explain concurrency collections and garbage collection in Java.

   • How do you profile an application for performance issues?

   • Discuss scalability and multithreading best practices.

10. SQL and Databases:

    • What are ACID properties in databases?

    • How do you perform query optimization in SQL?

    • What are the differences between manual queries and repository methods in projects?

    • Explain the difference between an index full scan and an index fast full scan.

11. OOP and Java 8 Features:

    • Explain OOP concepts like inheritance, polymorphism, and encapsulation.

    • How do Java 8 features like lambdas and streams work?

    • What is the difference between map() and flatMap() in Java 8?

    • How do you manage memory leaks in Java?

12. Miscellaneous Java Topics:

    • What are the most common bottlenecks in data loading into a machine?

    • How do you handle multiple interfaces that have the same method? What happens when you call this method?

    • Explain the Throwable hierarchy in Java.

    • What are try-catch-finally blocks, and what happens if System.exit() is called inside a catch block?

    • What are statics used for in Java?

Coding Problems:

1. Move Zeroes (LeetCode problem 283).

2. Return the maximum occurring character in an input string.

3. Find pairs with a sum equal to k from an array.

4. Count the occurrences of a character using Java 8.

5. Merge two sorted arrays and explain the time complexity.

6. Write a program to find vowels in an array of strings using Java 8.

7. Find duplicate elements in an array.

Additional Questions:

1. What are the rules for creating a table with the @Entity annotation in Hibernate?

2. How do you handle unit testing vs. integration testing in Spring Boot?

3. Explain the Kafka messaging system and the difference between a topic and a queue.

4. How do you handle a large number of exceptions in Spring controllers?

5. What is your experience with Redis for caching?

6. How does the garbage collector work in Java?