Initially asked about to introduce about myself.
Which language are u comfortable with?
What are the Java OOPS concepts?
What is meant by Encapsuation with realtime example?
What is meant by inheritance? Does java support multiple inheritance? 
How can it acheive multiple inheritance?
What is meant by Diamond problem?
What is meant by stack and Queue in detail?
Which data structure is used for the lift?
How do you implement multithreading(two ways)?
Which one is better either the Thread class or the Runnable interface and why?