OOP and Design Patterns: Discuss the four principles of Object-Oriented Programming (OOP). What design patterns have you used, and when would you apply them (e.g., Singleton, Factory)? Explain dependency injection and its advantages. Java Concurrency: Describe synchronized keyword and how it works. What are Callable and Future in Java concurrency? Explain the use of ThreadPoolExecutor and its importance in Java. Java 8+ Features: Describe lambda expressions and provide an example. Explain the purpose of Stream API and how it differs from traditional collections. What is Optional, and why is it useful? Framework-Specific Questions (Spring, Hibernate): Explain dependency injection in Spring. How does the Spring Boot application lifecycle work? Discuss Hibernate ORM and how it manages database transactions.