Explain core Java and Spring fundamentals

Java and Spring fundamentals

You are interviewing for a backend Java/Spring role. Answer the following conceptual questions:

1. Collections & data structures
   • Compare ArrayList and LinkedList in Java in terms of internal implementation, time complexity for common operations (access, insertion, deletion), and typical use cases.
2. Object-oriented design
   • Explain the SOLID design principles and give a short example for each principle.
3. Hash-based collections & concurrency
   • Compare Hashtable and HashSet : what does each store, how are keys/values handled, and what about thread safety?
   • Explain what ConcurrentHashMap is, how it differs from HashMap and Hashtable , and in what situations you would use it.
4. Strings and immutability
   • Compare String , StringBuilder , and StringBuffer in Java, including mutability and thread safety, and when you would use each.
   • What does it mean for an object to be immutable? Why can immutability be useful?
   • Describe how you would design and implement an immutable class in Java.
5. Concurrency primitives
   • Explain the purpose and behavior of the volatile keyword in Java. What problems does it solve and what are its limitations?
   • Explain what synchronization (the synchronized keyword) does in Java. How does it provide thread safety and what are the trade-offs?
   • Describe the java.util.concurrent.atomic package: what problem does it solve, and how do classes like AtomicInteger and AtomicReference work conceptually?
6. Exception handling
   • How should exceptions be handled in Java? Explain checked vs unchecked exceptions and discuss best practices for exception handling in real applications.
7. Spring core concepts
   • Explain Inversion of Control (IoC) and Dependency Injection (DI) in the context of the Spring framework, with an example of how dependencies are wired.
   • Explain Aspect-Oriented Programming (AOP) in Spring and give common use cases (for example, logging, transactions).
   • Describe how to define and use beans in Spring (for example, via annotations, Java configuration, or XML). How are beans created, managed, and injected?
   • Compare the stereotype annotations @Component , @Service , and @Repository in Spring. What do they have in common and when would you use each?
   • What other common Spring annotations do you know (such as @Controller , @RestController , @Autowired , @Qualifier , @Configuration , @Bean , @Transactional , etc.), and what are they used for?
8. Stream API
   • Explain how to use the Java Stream API to process collections (for example, filtering, mapping, grouping, and aggregation) in a functional style. Give a few examples of typical operations you would implement with streams.