java-developer.md

List of interview questions for Java Developer role

Java language and JVM

• Describe access modifiers (private, protected, public) and differences between them.
• What is inheritance?
• Describe difference between interface and abstract class.
• Is it possible that one class can be both abstract and final at the same time?
• Describe how does Garbage Collector works.
• What types Garbage Collector do we have? When to use which?
• Describe structure of Java Heap.
• Describe structure of JVM.
• What is the difference between Stack and Heap?
• Tell something about hashCode() and equals() methods. What contract they need to satisfy?
• Can hashCode() return constant value? Explain your answer.
• Can two objects have the same hashCode?
• When obj1.equals(obj2) is true, then is it possible that obj1 and obj2 have different hashCodes?
• Describe StringBuilder and StringBuffer classes. What are differences between them?
• Do you know java.util.concurrent package? Tell something about its contents.
• Do you know any frameworks for concurrent programming?
• Describe volatile keyword.
• Describe overriding and overloading. What are differences between them?
• Describe keywords final, finally and finalize().
• What is immutable object and how can you create it?
• Does all properties of immutable object need to be final?
• What is the difference between creating String with new operator and literal?
• Describe checked and unchecked exceptions. What are differences between them? When can we use specific type of exception and why?
• How does substring() works inside?
• Which method you need to implement to use object as key in a HashMap?
• Where do equals and hashcode come in the picture during get(...) operation?
• What's the difference between Executor.submit() and Executor.execute() method
• Can you write thread-safe Singleton?
• Write code iterating over HashMap
• Is it better to synchronize critical section of getInstance() or whole getInstance() method?
• What's wrong with using HashMap in multithreaded environment?
• How to create, start, destroy and block Threads in Java?
• Do you know any thread-safe collections?
• How would you prevent client from directly instantiation your concrete class?
• What's the difference between HashMap and HashTable?
• How does HashMap works?
• Describe shortcuts: JNI, JNDI, JAAS
• Describe differences between Filter and Servlet
• Does LocalDateTime have information about time zone? If not, then how to define time zone?
• What are differences between Array and ArrayList?
• When should we use LinkedList and when ArrayList?
• How to change a value of the final class with immutable attributes?

Spring

• What bean scopes do we have?
• What's default bean scope?
• How many instances bean has by default?
• How can we wire beans and components?
• How can we inject components?
• How Spring wires components and beans under the hood?
• What's new in Spring Boot when we compare it to Spring Core
• What @SpringBootApplication annotation has under the hood?
• When we explicitly call a method without any annotation, which calls internally a method with @Transactional annotation, then the whole operation will be transactional? Explain why?
• Why injecting components via constructor (with @Autowired annotation) is better than injecting them via annotations on class attributes?
• When should we use aspects?
• How to create aspect and what should it have?
• How to create async operations?
• How to schedule operations?

Design Patterns

• What design patterns do you know?
• Describe facade/adapter/builder/{any} pattern.
• What's the difference between factory and abstract factory pattern?
• What is Singleton?

Good software development practices

• What good practices of software development do you know?
• When you take a look at the code how do you recognize if it's clean and well written?
• How would you design method in the right way?
• What is loose coupling?
• What is recommended maximum number of lines in the method?

Programming Paradigms

• Describe structural programming paradigm
• Describe Object-Oriented Programming paradigm
• Describe functional programming paradigm
• Describe reactive programming paradigm

Multi-threading & Concurrency

• What problems can we solve with multi-threaded programs?
• What problems do we have during writing multi-threaded programs?
• How to deal with problems occurring in multi-threaded programs?
• What multi-threaded programming models do you know?
• How do you implement different multi-threaded programming models in Java?
• How to deal with shared data model in multi-threaded environment?

Version Control Systems

• What kind of Version Control Systems do you know?
• Do you think Git is better than other systems? Why?
• Can you work offline with Git?
• Can you work offline with SVN?

Continuous Integration

• What types of Continous Integration Servers do you know? Have you used any?
• How did you used Jenkins or other CI Server in your work?

Software development methodologies

• In what methodologies did you work?
• Do you know scrum? Describe it.
• Can you describe kanban model?
• Can you describe waterfall model?

Testing

• What types of tests do you know?
• What is the difference between mock and stub?
• Do you know any libraries for mocking? Describe them.
• Do you know any libraries for testing? Describe them.
• What annotations of JUnit do you know and what is their purpose?
• How would you test method, which has to use implementation of method from another class, which is not ready yet?

Web Services

• Describe SOAP.
• Describe REST.
  • What request methods can you use for getting/inserting/updating/deleting data?
  • What is common protocol for REST
  • How good RESTful end-point should look like?
  • What are principles of designing good RESTful API?

Others

• What operating system do you prefer and why?
• What are news introduced in Java 8/9/10/11?
• What technical book did you read recently?
• What are your methods for learning new things?