Java Technical Interview Questions

Core Java Concepts

• 1. What is the difference between JDK and JRE?
• 2. Why is Java a platform independent language?
• 3. What is the difference between an abstract class and an interface?
• 4. What is the difference between final, finally, and finalize?
• 5. What is the difference between stack and heap memory?
• 6. What is the difference between method overloading and method overriding?
• 7. What is the difference between an abstract class and an interface?
• 8. What is the difference between a private and a protected modifier?
• 9. What is constructor overloading in Java?
• 10. What is the use of super keyword in Java?
• 11. What is the difference between static methods, static variables, and static classes in Java?
• 12. What exactly is System.out.println in Java?
• 13. What part of memory - Stack or Heap - is cleaned in the garbage collection process?

Object-Oriented Programming

• 1. What are the Object Oriented Features supported by Java?
• 2. What are the different access specifiers used in Java?
• 3. What is the difference between composition and inheritance?
• 4. What is the purpose of an abstract class?
• 5. What are the differences between constructor and method of a class in Java?
• 6. What is the diamond problem in Java and how is it solved?
• 7. What is the difference between local and instance variables in Java?
• 8. What is a Marker interface in Java?

Data Structures and Algorithms

• 1. Why are strings immutable in Java?
• 2. What is the difference between creating a String using new() and as a literal?
• 3. What is the Collections framework?
• 4. What is the difference between ArrayList and LinkedList?
• 5. What is the difference between a HashMap and a TreeMap?
• 6. What is the difference between a HashSet and a TreeSet?
• 7. What is the difference between an Iterator and a ListIterator?
• 8. What is the difference between an ArrayList and a LinkedList?
• 9. What is the purpose of the Comparable interface?
• 10. What is the difference between a HashSet and a TreeSet?
• 11. What is the purpose of the java.util.concurrent package?

Exception Handling

• 1. What is an exception?
• 2. How does an exception propagate throughout the Java code?
• 3. What is the difference between checked and unchecked exceptions?
• 4. What is the use of try-catch block in Java?
• 5. What is the difference between throw and throws?
• 6. What is the use of the finally block?
• 7. What’s the base class of all exception classes?
• 8. What is Java Enterprise Edition (Java EE)?
• 9. What is the difference between a Servlet and a JSP?
• 10.What is the purpose of the Java Persistence API (JPA)?
• 11.What is the difference between stateful and stateless session beans?

Multithreading

• 1. What is a thread and what are the different stages in its lifecycle?
• 2. What is the difference between process and thread?
• 3. What are the different types of thread priorities available in Java?
• 4. What is context switching in Java?
• 5. What is the difference between user threads and Daemon threads?
• 6. What is synchronization?
• 7. What is a deadlock?
• 8. What is the use of the wait() and notify() methods?
• 9. What is the difference between a thread and a process in Java?
• 10. What is the difference between synchronized and volatile in Java?
• 11.What is the purpose of the sleep() method in Java?
• 12.What is the difference between wait() and sleep() in Java?
• 13.What is the difference between notify() and notifyAll() in Java?