Cognizant interview questions

Explain the OOPs concepts in detail.

basically it was technical interview, it's a 20 minutes, i was asked to give a self intro, explain oops concepts in detail(with example), asked me rate on java out 5 , i answered 4, then interview asked write a Fibonacci series using recursion, queations on collection framework (what is it, examples, difference between arraylist and arrays, what is hashmap explain about it and difference between stack and queue) , what is comparator and comparable, asked me explain and to go through file handling process and some SQL questions like what is different type keys, difference drop, truncate and delete .