Prajwalraj IT Solutions Software Engineer - Java Developer interview questions

Sure! Here's a well-organized list of **Java Developer Interview Questions**, grouped by topic: --- ## 🔹 Core Java 1. **What is the difference between `==` and `.equals()` in Java?** 2. **Explain OOP principles** with examples (Abstraction, Encapsulation, Inheritance, Polymorphism). 3. **What is a constructor?** Can it be private? 4. **What is the difference between `ArrayList` and `LinkedList`?** 5. **How does `HashMap` work internally?** 6. **What is the difference between `String`, `StringBuilder`, and `StringBuffer`?** 7. **What is a static block? When does it execute?** 8. **What is the difference between checked and unchecked exceptions?** 9. **What are `final`, `finally`, and `finalize()`?** 10. **What is the difference between `abstract class` and `interface`?** --- ## 🔹 Java 8 Features 1. **What is a Lambda Expression? Give syntax.** 2. **What is the Stream API? How is it useful?** 3. **What is a Functional Interface?** 4. **Difference between `map()` and `flatMap()`?** 5. **How does `Optional` work?** --- ## 🔹 Multithreading & Concurrency 1. **What is the difference between `Runnable` and `Thread`?** 2. **What is a daemon thread?** 3. **Explain thread lifecycle.** 4. **What is synchronization? Why is it used?** 5. **What are `wait()`, `notify()`, and `notifyAll()`?** --- ## 🔹 Collections Framework 1. **Difference between `HashMap` and `Hashtable`** 2. **Difference between `Set` and `List`** 3. **What is the difference between `TreeSet` and `HashSet`?** 4. **When do we get `ConcurrentModificationException`?** 5. **How does `HashSet` ensure uniqueness?** --- ## 🔹 Spring & Spring Boot 1. **What is Spring Boot? How is it different from Spring?** 2. **What is Dependency Injection (DI)?** 3. **What are the commonly used annotations in Spring Boot?** 4. **What is the use of `@Autowired` and `@Qualifier`?** 5. **How do you create a REST API in Spring Boot?** 6. **What is the use of `application.properties` file?** 7. **What is the difference between `@Component`, `@Service`, and `@Repository`?** --- ## 🔹 Hibernate / JPA 1. **What is ORM? How does Hibernate help?** 2. **What are the differences between `get()` and `load()` methods?** 3. **What is the difference between lazy and eager loading?** 4. **Explain primary annotations in Hibernate: `@Entity`, `@Id`, `@Table`, etc.** 5. **What are the states of a Hibernate object? (Transient, Persistent, Detached)** --- ## 🔹 SQL & Database 1. **Write a SQL query to fetch the second highest salary.** 2. **What is the difference between `INNER JOIN` and `LEFT JOIN`?** 3. **What is normalization? What are the different normal forms?** 4. **How do you handle transactions in SQL?** 5. **What is an index? When should you use it?** --- ## 🔹 Coding Questions (Common in Interviews) 1. **Reverse a string without using built-in methods.** 2. **Find duplicate elements in an array.** 3. **Check if a number is a palindrome.** 4. **Implement a simple LRU cache in Java.** 5. **Find the missing number in an array of 1 to N.** --- Would you like sample **answers**, or a **PDF file** for this list? I can also give you a **mock interview** based on this.