Top 30 Java Support Interview Questions (2025)

Here’s an updated list of Top 30 Java Support Interview Questions (2025), tailored for candidates applying for Java support roles. These questions cover a wide range of topics, including basic Java concepts, object-oriented programming (OOP), exception handling, collections, multi-threading, and tools commonly used in production environments.

Basic Java and OOP Concepts

1. What is Java and how does it differ from other programming languages?
   • Explain key features like platform independence, security, and object-oriented nature.
2. What are the main differences between JDK, JRE, and JVM?
   • Discuss the roles of the Java Development Kit, Java Runtime Environment, and Java Virtual Machine in a Java application.
3. What is the difference between a class and an object in Java?
   • Define classes and objects, and explain how they relate to each other in Java.
4. What is the significance of static keyword in Java?
   • Explain the use of static variables, methods, and blocks, including their behavior across class instances.
5. What is the difference between == and equals() in Java?
   • Discuss the difference between comparing object references (==) and object contents (equals()).
6. What is an abstract class and how does it differ from an interface?
   • Provide examples to explain when to use an abstract class versus an interface.

Java Memory Management and Garbage Collection

7. What is the Java heap and stack memory?
   • Explain how memory is allocated for objects and primitives in Java, and how the JVM handles memory.
8. What is garbage collection in Java? How does it work?
   • Discuss the concept of garbage collection and the different algorithms (Mark-and-Sweep, Generational GC, etc.).
9. What are memory leaks in Java, and how can they be avoided?
   • Explain common causes of memory leaks and techniques to detect and resolve them.
10. How does the JVM handle object memory allocation?
    • Describe how objects are created in the heap and the role of the garbage collector.

Java Exception Handling

11. What are exceptions in Java? What is the difference between checked and unchecked exceptions?
    • Provide examples of both checked and unchecked exceptions, and explain when to use them.
12. How does Java handle exception propagation?
    • Discuss how exceptions propagate through method calls and how throws and throw are used.
13. What is the purpose of the finally block in exception handling?
    • Explain how the finally block ensures the execution of code after a try-catch block.
14. What is the difference between throw and throws in Java?
    • Define and explain the use of throw for throwing exceptions and throws for declaring them.
15. What is a custom exception in Java, and how do you create one?
    • Describe how to create custom exception classes by extending the Exception class.

Java Collections and Data Structures

16. What is the difference between List, Set, and Map in Java Collections?
    • Compare and contrast the three major interfaces in the Java Collections Framework.
17. What is the difference between ArrayList and LinkedList in Java?
    • Explain when to use ArrayList versus LinkedList based on performance considerations.
18. What is the HashMap and how does it work internally?
    • Explain the underlying data structure of HashMap and the concept of hashing.
19. What is the difference between HashMap and TreeMap in Java?
    • Discuss the ordering and performance differences between HashMap and TreeMap.
20. What is the difference between Iterator and ListIterator in Java?
    • Compare the functionality and methods provided by Iterator and ListIterator.

Java Multi-Threading and Concurrency

21. What is the difference between a process and a thread in Java?
    • Explain the basic concepts of processes and threads and how they interact in Java.
22. What are some common thread synchronization techniques in Java?
    • Discuss the use of synchronized blocks, ReentrantLock, and Semaphore for thread synchronization.
23. What is the volatile keyword in Java?
    • Explain how volatile ensures visibility of changes to variables across threads.
24. What is the difference between wait() and sleep() in Java?
    • Discuss how both methods work and how they affect thread execution.
25. What is the ExecutorService and how does it help in Java concurrency?
    • Explain the purpose of the ExecutorService for managing thread pools and asynchronous task execution.
26. What is a deadlock in Java, and how can you avoid it?
    • Define deadlock and provide strategies for preventing it in multi-threaded applications.

Java 8 and Beyond Features

27. What are the new features introduced in Java 8?
    • Discuss important Java 8 features such as Lambda expressions, the Stream API, and the Optional class.
28. What is a Stream in Java, and how do you use it?
    • Explain how to create and process streams of data in a functional programming style with the Stream API.
29. What is the Optional class in Java 8, and when should it be used?
    • Discuss how the Optional class helps handle null values and improve code readability.
30. What are default and static methods in interfaces in Java 8?
    • Explain the ability to define methods with implementations inside interfaces using default and static.

Additional Support and Troubleshooting Questions

31. How would you troubleshoot a Java application that is running out of memory?
    • Discuss memory analysis techniques such as heap dumps, profiling, and tools like VisualVM and Eclipse MAT.
32. What are some common performance bottlenecks in Java applications, and how do you optimize them?
    • Discuss profiling techniques, memory optimizations, garbage collection tuning, and database optimization.
33. What tools can you use to monitor a Java application in a production environment?
    • Mention tools like JConsole, VisualVM, Prometheus, and Grafana for monitoring and diagnosing production systems.
34. What is thread pooling, and why is it important in Java?
    • Explain the benefits of thread pooling using the ExecutorService and how it improves resource management.
35. How would you handle database connection pooling in a Java application?
    • Discuss the use of connection pools like HikariCP or Apache Commons DBCP to manage database connections efficiently.
36. How would you handle logging in a Java application?
    • Discuss logging frameworks like Log4j, SLF4J, and Logback, and the importance of log levels and rolling file appenders.
37. How can you debug a Java application remotely?
    • Explain techniques such as remote debugging with tools like IntelliJ IDEA or Eclipse, and the use of jdb for remote Java debugging.
38. What is the role of JNDI in a Java application?
    • Explain the Java Naming and Directory Interface (JNDI) and how it’s used for accessing services such as databases and EJBs.
39. What is the difference between StringBuilder and StringBuffer?
    • Explain the thread-safety and performance differences between StringBuilder and StringBuffer.
40. What is the difference between equals() and hashCode() methods in Java?
    • Discuss how equals() and hashCode() are used to compare objects and the importance of implementing them correctly in collections.

Conclusion

These 30 Java support interview questions are designed to test a broad range of knowledge, from basic Java syntax and object-oriented principles to advanced topics like concurrency, Java 8 features, and troubleshooting Java applications in production environments. Be prepared to answer questions related to debugging, performance optimization, and using Java frameworks and tools effectively.