Program output you have tell. And why you have to explain? Some basic questions will be asked like:- What is the difference between JDK, JRE, and JVM? ... What is a JIT compiler? ... What are Brief Access Specifiers and Types of Access Specifiers? ... How many types of constructors are used in Java? ... Can a constructor return a value? ... Explain 'this' keyword in Java. Oops concept question will be asked. Thread concept question will be asked. Finally Collection framework questions will be asked. If you know front end then be prepared according to front end pattern.