In this post, I'm going to cover questions that are really popular among the interviewers for a Java Developer position. I'm a Java Developer with around 7 years of experience and I've prepared a list of questions with my interview experiences that are a must for every Java Interview. If you are going for an interview, you should brush up below questions.

Must Interview Questions for Java Developer

Core Java

What are OOPs? Difference between Encapsulation and Abstraction. See Answer Here
What is String Pool? See Answer Here
What is the difference between Inheritance and Composition? Which one we should use when?
What are SOLID principles?
How many ways are there to create an Object?
What are marker interfaces? Why do we need them? How does JVM identify a marker interface?
What are the new features of the newest Java version that you are currently using?
Questions on Lambda expressions

Advanced Java

Differentiate between Arraylist, LinkedList, and HashSet.
How does HashSet work internally? How does it maintain uniqueness?
What is ConcurrentHashMap? Differentiate between HashTable, HashMap, and ConcurrentHashMap. How does ConcurrentHashMap work internally?
What is a Singleton class? How do you create a Singleton class? How do you break a Singleton class? How to create a Singleton class for a multithreaded environment?
How many ways are there to create a Thread? Which one to use and why?

Spring and Spring Boot

What is Dependency Injection?
How many ways to inject beans? Which one is best and why?
What is the default bean scope? How to change/define the scope of a bean?
How does RequestMapping annotation work internally?
How to enable transactions? What's the benefit of using transactions?
What are Aspect, Advice, PointCut, and JoinPoint in AOP?
How to disable a specific auto-configuration? How to register a custom auto-configuration?
What is ConditionalOnMissingBean annotation?
Why do we need Spring Profiles?
Which is better - Properties or YAML? Why?