Panamax Infotech interview question

oop , abstraction encapsulation, java 8 features, default method what's is necessity of interface over abstract class, internal working of hashmap, serialization, transistent keyword, polymorphism, multithreading concept, t1.start() t1.start() t1.run() , synchronization, why string is immutable, program to sort array without any inbuilt method or algorithm, hibernate, lastly one SQL query of self join