OpenText Senior Java Developer interview questions

In team lead interview he asked me about the challanges I have faced previously. And also a coding exercise

What annotations have you used with SpringSecurity? What is @SpringBootApplication? What is @EnableAutoconfiguration What is @Component What is bean scope? How do you make a bean Singleton? What is lazy and eager initialization in singleton? What is double checked singleton? Why use double check? What is volatile keyword? What is chaining in Java 8? Given a string, print first non repetitive character using Java 8. Given a list of integers. Print non duplicate values using Java 8. How do you make system fault tolerant in micro services? What is fallback mechanism if service 1 is calling service 2 and service 2 is down. Kafka command to create, consume and product topic? What is synchronized hashmap? What is thread pooling? There is 50 tasks, we do not want to create 50 threads to do them. How to proceed? How to do memory management in java? What memory areas are available? new String vs string literal Static variables go in stack or on heap? Equals and hashcode method contract in HashMap?