Core Java Interview Questions and Answers

Ques 151. How are Observer and Observable used?

Ans. Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.

Ques 152. Can a lock be acquired on a class?

Ans. Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.

Ques 153. What state does a thread enter when it terminates its processing?

Ans. When a thread terminates its processing, it enters the dead state.

Ques 154. How does Java handle integer overflows and underflows?

Ans. It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

Ques 155. What is the difference between the >> and >>> operators?

Ans. The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have been shifted out.