Java Interview Questions and Answers
|
|
-
What is an applet?-
Applet is a dynamic and interactive program that runs inside a web page
displayed by a java capable browser.
-
What is the difference
between applications and applets?-
a)Application must be run on local machine whereas applet needs no explicit
installation on local machine. b)Application must be run explicitly within a
java-compatible virtual machine whereas applet loads and runs itself
automatically in a java-enabled browser. d)Application starts execution with
its main method whereas applet starts execution with its init method.
e)Application can run with or without graphical user interface whereas applet
must run within a graphical user interface.
-
How does applet
recognize the height and width?-
Using getParameters() method.
|
|
|
|
|
-
When do you use codebase
in applet?-
When the applet class file is not in the same directory, codebase is used.
-
What is the lifecycle of
an applet?-
init() method - Can be called when an applet is first loaded start() method -
Can be called each time an applet is started. paint() method - Can be called
when the applet is minimized or maximized. stop() method - Can be used when the
browser moves off the applet’s page. destroy() method - Can be called when the
browser is finished with the applet.
-
How do you set security
in applets?-
using setSecurityManager() method
|
|
|
|
|
-
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
-
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.
-
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.
|
|
|
|
|
-
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() .
-
What is meant by
controls and what are different types of controls in AWT?-
Controls are components that allow a user to interact with your application and
the AWT supports the following types of controls: Labels, Push Buttons, Check
Boxes, Choice Lists, Lists, Scrollbars, Text Components. These controls are
subclasses of Component.
-
What is the difference
between choice and list?-
A Choice is displayed in a compact form that requires you to pull it down to
see the list of available choices and only one item may be selected from a
choice. A List may be displayed in such a way that several list items are
visible and it supports the selection of one or more list items.
|
|
|
|
|
-
What is the difference
between scrollbar and scrollpane?-
A Scrollbar is a Component, but not a Container whereas Scrollpane is a
Conatiner and handles its own events and perform its own scrolling.
-
What is a layout manager
and what are different types of layout managers available in java AWT?-
A layout manager is an object that is used to organize components in a
container. The different layouts are available are FlowLayout, BorderLayout,
CardLayout, GridLayout and GridBagLayout.
-
How are the elements of
different layouts organized?-
FlowLayout: The elements of a FlowLayout are organized in a top to bottom, left
to right fashion. BorderLayout: The elements of a BorderLayout are organized at
the borders (North, South, East and West) and the center of a container.
CardLayout: The elements of a CardLayout are stacked, on top of the other, like
a deck of cards. GridLayout: The elements of a GridLayout are of equal size and
are laid out using the square of a grid. GridBagLayout: The elements of a
GridBagLayout are organized according to a grid. However, the elements are of
different size and may occupy more than one row or column of the grid. In
addition, the rows and columns may have different sizes.
|
|
|
|
|
|