An exception is an abnormal condition that arises in a code sequence at run time. Basically there are four important keywords which form the main pillars of exception handling: try, catch, throw and finally. Code which you want to monitor for exception is contained in the try block. If any exception occurs in the try block its sent to the catch block which can handle this error in a more rational manner. To throw an exception manually you need to call use the throw keyword. If you want to put any clean up code use the finally block. The finally block is executed irrespective if there is an error or not.