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Java Swing interview questions – Part 2

Java Swing/AWT interview questions โ€“ Part 2

16. What is the difference between invokeAndWait() and invokeLater()?
invokeAndWait is synchronous. It blocks until Runnable task is complete. InvokeLater is asynchronous. It posts an action event to the event queue and returns immediately. It will not wait for the task to complete

17. Why should any swing call back implementation execute quickly?
Callbacks are invoked by the event dispatch thread. Event dispatch thread blocks processing of other events as long as call back method executes.

18. What is an applet?
Applet is a java program that runs inside a web browser.

19. What is the difference between applications and applets?
Application must be run explicitly within Java Virtual Machine whereas applet loads and runs itself automatically in a java-enabled browser. Application starts execution with its main method whereas applet starts execution with its init method. Application can run with or without graphical user interface whereas applet must run within a graphical user interface. In order to run an applet we need a java enabled web browser or an appletviewer.

20. Which method is used by the applet to recognize the height and width?

21. When we should go for codebase in applet?
If the applet class is not in the same directory, codebase is used.

22. What is the lifecycle of an applet?
init( ) method – called when an applet is first loaded
start( ) method – called each time an applet is started
paint( ) method – called when the applet is minimized or maximized
stop( ) method – called when the browser moves off the applet’s page
destroy( ) method – called when the browser is finished with the applet

23. Which method is used for setting security in applets?

24. What is an event and what are the models available for event handling?
Changing the state of an object is called an event. An event is an event object that describes a state of change. In other words, event occurs when an action is generated, like pressing a key on keyboard, clicking mouse, etc. There different types of models for handling events are event-inheritance model and event-delegation model

25. What are the advantages of the event-delegation model over the event-inheritance model?
Event-delegation model has two advantages over event-inheritance model. a)Event delegation model 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 event-delegation model does not have to be repeatedly process unhandled events as is the case of the event-inheritance.

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

27. What is controls and what are different types of controls in AWT?
Controls are components that allow a user to interact with your application. AWT supports the following types of controls: Labels, Push Buttons, Check Boxes, Choice Lists, Lists, Scrollbars, Text Components. These controls are subclasses of Component.

28. 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.

29. What is the difference between scrollbar and scrollpane?
A Scrollbar is a Component, but not a Container whereas Scrollpane is a Container and handles its own events and perform its own scrolling.

30. What is a layout manager and what are different types of layout managers available?
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 , GridBagLayout, Boxlayout and SpringLayout


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One Response to “Java Swing interview questions – Part 2”

  1. very helpful… ๐Ÿ™‚

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