Java Interview Questions for 3 Years Experience

Top 25 Java Interview Questions for 3 Years Experience (Expert Answers)

Are you preparing for a Java interview with 3 years of experience?
This guide covers the most asked Java interview questions for 3 years experience across Core Java, Java 8, Spring Boot, Collections, and more, with clear answers and code examples.

Java Interview Questions for 3 Years Experience
Java Interview Questions for 3 Years Experience

πŸ”Ή Core Java & OOPs Interview Questions

1. What are the main principles of Object-Oriented Programming?

The four core principles of OOP are:

  • Encapsulation
  • Inheritance
  • Polymorphism
  • Abstraction

2. What is the difference between == and .equals() in Java?

  • == checks reference equality
  • .equals() checks value equality
javaCopyEditString a = new String("Hello");
String b = new String("Hello");

System.out.println(a == b);       // false
System.out.println(a.equals(b));  // true

3. Explain method overloading vs. overriding.

  • Overloading: Compile-time polymorphism (same method name, different params)
  • Overriding: Runtime polymorphism (subclass redefines parent method)

4. Can a constructor be final?

No. Constructors can’t be final because they are never inherited.

πŸ”Ή Java 8 & Stream API Questions

5. What is a functional interface?

An interface with exactly one abstract method.

javaCopyEdit@FunctionalInterface
interface MyFunc {
    void run();
}

Used with lambda expressions.

6. What features were introduced in Java 8?

  • Lambda expressions
  • Stream API
  • Functional interfaces
  • Default & static methods in interfaces
  • Optional class
  • New Date & Time API

7. Stream API example to filter even numbers?

javaCopyEditList<Integer> numbers = Arrays.asList(1, 2, 3, 4);
List<Integer> evens = numbers.stream()
    .filter(n -> n % 2 == 0)
    .collect(Collectors.toList());

πŸ”Ή Exception Handling

8. Difference between throw and throws?

  • throw: Used to manually throw an exception
  • throws: Declares potential exceptions in method signature

9. Checked vs. Unchecked Exceptions?

  • Checked: Checked at compile time (IOException)
  • Unchecked: Runtime exceptions (NullPointerException)

10. What is the finally Block used for?

To execute code regardless of exception, often used to close resources.

πŸ”Ή Spring Boot Questions

11. What is Spring Boot?

A framework that simplifies Spring applications:

  • Embedded servers
  • Auto-configuration
  • Minimal setup

12. Difference between @Component, @Service, @Repository?

  • @Component: Generic bean
  • @Service: Business logic
  • @Repository: Data access layer

13. What is dependency injection?

A design pattern where the framework injects objects into classes instead of you manually instantiating them.

14. Use of application.properties?

To externalise configuration.

propertiesCopyEditserver.port=8080
spring.datasource.url=jdbc:mysql://localhost:3306/test

πŸ”Ή Java Collections

15. Difference between ArrayList and LinkedList?

FeatureArrayListLinkedList
Access timeFastSlower
InsertionSlowerFaster
StorageLess overheadMore memory

16. How does HashMap work internally?

  • Uses hashCode and equals
  • Keys go into buckets
  • Collisions handled via linked list (or tree from Java 8)

17. Difference between HashMap and Hashtable?

  • HashMap: Not synchronised
  • Hashtable: Synchronised, slower

πŸ”Ή Multithreading

18. Difference between synchronised method and block?

  • Method: Locks the entire method
  • Block: Locks only a section of code or an object

19. What is the volatile keyword?

Ensures the variable is read from main memory, not the thread-local cache.

20. Difference between wait(), sleep(), join()?

  • wait(): Waits and releases lock
  • sleep(): Waits without releasing lock
  • join(): Waits for a thread to die

πŸ”Ή Behavioural / Real-Life Questions

21. Have you used Git in projects?

Yes, for:

  • Version control
  • Feature branching
  • Pull request-based reviews

22. How do you debug production issues?

  • Log analysis
  • Stack trace reading
  • Tools like ELK, Splunk

23. Experience with REST APIs?

  • Built using @RestController
  • JSON handling
  • Consumed via RestTemplate or WebClient

24. Java Interview Questions for 3 Years Experience on Unit Testing

  • JUnit 5
  • Mockito
  • Coverage via IntelliJ or Jacoco

25. Why should we hire you?

  • 3 years Java experience
  • Strong in Spring Boot, Java 8
  • Clean code, REST, Git, Testing
  • Proactive and team-driven

πŸ“˜ More Helpful Resources

❓ FAQs

What topics are important for 3 years Java experience?

Core Java, Java 8, Collections, Spring Boot, REST APIs, SQL.

Is 3 years of experience enough for mid-level Java roles?

Yes. You are expected to know frameworks, APIs, OOPs, and be production-ready.

How to prepare fast for a Java interview?

Practice real Q&A, revise Java 8, do mock interviews, and study system design basics.

It is always advised to read official documents for building a better understanding.

Official Java docs:
πŸ‘‰ https://docs.oracle.com/javase/tutorial/

Spring docs:
πŸ‘‰ https://spring.io/guides

πŸ“© Got a Question?

Drop your queries in the comments or contact us here.
We’ll help you crack your next Java interview! πŸš€

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