Java ----- Are there destructors in Java? How do you call them? Difference between finally and finalize? Can you call finalize() whenever you want? C++ OOP ---- With regards to Insertions and Deletions, why is LinkedList better than a Dynamic Array? OS ---- What is Mutex? Math ----- Birthday problem: 400 people same birthday in a year What is sum to n natural numbers? Can you derive it? What is pigeonhole principle?