Java Interview Questions 49

241. How do you set security in applets?
Ans. using setSecurityManager() method

242. What is an event and what are the models available for event handling?- An
event is an event object that describes a state of change in a source. In other
words, event occurs when an action is generated, like pressing button, clicking
mouse, selecting a list, etc. There are two types of models for handling events and
they are: a) event-inheritance model and b) event-delegation model

243. What are the advantages of the model over the event-inheritance model?- The event-delegation model has two advantages over the event-inheritance model. They
are: a)It enables event handling by objects other than the ones that generate the
events. This allows a clean separation between a component’s design and its use.
b)It performs much better in applications where many events are generated. This
performance improvement is due to the fact that the event-delegation model does not
have to be repeatedly process unhandled events as is the case of the
event-inheritance.

244. What is source and listener?- source : A source is an object that generates
an event. This occurs when the internal state of that object changes in some way.
listener : A listener is an object that is notified when an event occurs. It has
two major requirements. First, it must have been registered with one or more
sources to receive notifications about specific types of events. Second, it must
implement methods to receive and process these notifications.

245. What is adapter class?- An adapter class provides an empty implementation
of all methods in an event listener interface. Adapter classes are useful when you
want to receive and process only some of the events that are handled by a
particular event listener interface. You can define a new class to act listener by
extending one of the adapter classes and implementing only those events in which
you are interested. For example, the MouseMotionAdapter class has two methods,
mouseDragged()and mouseMoved(). The signatures of these empty are exactly as
defined in the MouseMotionListener interface. If you are interested in only mouse
drag events, then you could simply extend MouseMotionAdapter and implement
mouseDragged() .