Focus on core java - Really Important. Deep implementation on Data structures like questions can be How does search implemented in Array list ? and how is it difference with regards to HashMap ? Why interfaces are created when you have abstract concepts ? ? Few basic questions on polymorphism, perhaps a quick review on OOP concepts would do. Questions on all kinds of indexing algorithms & Cache related questions Reasons of introducing new features from java version to version ( 8, 11, 17, 21 )