Section 1.1: Project Flow and Architecture

In this segment, I aim to assess the candidate's experience. If the candidate is inexperienced, I will delve deeper into their project to understand its functionality, flow, architecture, tech stack, and deployment process, along with their specific contributions.

Typical questions might include:

• Can you describe your project and its architecture? Please explain and illustrate the architecture, frameworks, and technologies utilized.
• Document everything you know about your project to avoid being overwhelmed. Remember, you are the expert on your project—be confident!

Section 1.2: Core Java Fundamentals

Core Java encompasses a broad range of topics, and interviewers will focus on key areas. Providing thorough responses in this domain is crucial, as lacking knowledge in Core Java can be detrimental, even if you know various frameworks.

Key topics often discussed include:

• String Concepts / Hashcode-Equals Methods
• Immutability (custom immutable classes and examples in JDK)
• OOP Principles (all four pillars and SOLID principles)
• Serialization (serialVersionUID)
• Collection Framework (including Concurrent Collections such as HashMap, ConcurrentHashMap, ArrayList, HashSet)
• Exception Handling (especially Runtime Exceptions)
• Multithreading, particularly the Executor Framework (including ThreadPool, deadlock, and Thread-dump)
• Java Memory Model (storage of objects, methods, and variables)
• Garbage Collection (how it works, object collection, and algorithms involved)

Here are sample questions:

• How does ThreadPoolExecutor function?
• How would you create a custom immutable class? What are examples of immutable classes in Java?
• Can you explain hashCode() and equals()? What happens if you use a custom Object as a key in a map? How can you do this correctly?
• What are deep copy and shallow copy?
• What is CompletableFuture?
• Can you explain the Java Memory Model according to the latest Java version?
• What is a concurrent collection?
• What are the time/space complexities of HashMap, ArrayList, and LinkedList?
• What algorithms do Java APIs like Arrays.sort() and Collections.sort() utilize?
• How would you create a custom annotation in Java?
• How do HashMap and HashSet operate internally?
• What is the purpose of String's join() method?

For further reference, check out the article linked above.

Section 1.3: Java 8/Java 11/Java 17 Features

Familiarity with significant features of newer Java versions is essential. You can consult my article that documents updates from Java 8 through Java 21.

Key topics include:

• Java 8 Features: Default/Static Methods, Lambda Expressions, Functional Interfaces, Optional API, Stream API, Pattern Matching, Text Blocks, and Modules.

Be prepared to discuss:

• What’s new in Java 8, Java 11, and Java 17?
• What is a parallel stream in Java, and how does it function?
• What enhancements have been made to the Java memory model, particularly concerning Java 8’s HashMap?

Section 2.1: Spring Framework and Microservices Overview

This topic encompasses both basic and advanced questions that often arise in interviews. Mastery in Spring Framework, Spring Boot, Microservices, and REST APIs is crucial, as a failure to satisfy the interviewer on these subjects may lead to rejection.

Key areas to cover include:

• Dependency Injection / Inversion of Control (IoC)
• Spring MVC Configuration and Annotations
• CRUD Operations
• Bean Scopes and Lifecycle
• AOP, Exception Handling, and Control Advice
• Security (JWT, OAuth)
• Actuators
• WebFlux and Mono Framework
• Microservice Concepts
• Spring Cloud
• JPA

Sample questions may include:

• What are the functions of the annotations @RequestMapping, @RestController, @Service, @Repository, and @Entity?
• Can you explain what an Actuator is and its uses?
• How do you ensure your application is fault-tolerant and resilient?
• What is distributed tracing, and what roles do traceId and spanId play in a Spring Boot application?
• What is WebFlux, and how does it relate to the Mono Framework in Spring Boot?
• How do you manage cyclic dependencies in Spring?
• What strategies do you employ to secure REST APIs?

Section 3.1: Understanding Databases with Hibernate

This section addresses the data layer where Hibernate and JPA frameworks come into play. Interviewers with a strong background in databases may probe deeply into this area, so be prepared to demonstrate your knowledge and write queries.

Key topics include:

• JPA Repositories
• Entity Relationships
• SQL Queries (e.g., Employee department queries, Highest Nth salary queries)
• Relational and Non-Relational DB Concepts
• CRUD Operations in Databases

Common questions might involve:

• What distinguishes SQL from NoSQL databases?
• Can you explain sharding in databases?
• What is JPA, and how does it function?
• Describe the Parent-Child relationship in entities.
• What are joins, and how do they work?

For additional insights, refer to the related articles.