Nuvalence interview question

Describe the most complex project you've worked on using spring and java. How do you approach a difficult problem and the tools you use. Describe a difficult problem you encountered and how you solved it. What do I like/dislike about Java and Spring what I would change about them. How would you explain concurrency to a junior developer. What are the benefits of object oriented programming. How do you use NULL in Java. Why would you use it.