Infobrain Technologies Java Developer Fresher interview questions

I went through a reference. I am a postgraduate trained on Java technology. I had two technical rounds. 1st round ) : Interview question were so easy from....OOPS Concept(write program for inheritance,constructors, polymorphism),multithreading concept & collection frameworks(Map Interface). In 2nd technical rounds : They asked me more questions from Data Structures...Sorting(only few) & also asked to write program for prime numbers. I didn't remember Wts prime no. But HR gave me clue but could not write the logic. So...I was not shortlisted.