AWT and Swing Interview Questions are part of any Java interviews which
involves GUI development work. Since AWT(Abstract Windows
Toolkit) and Swing offers most popular Java GUI solutions, Yes,
JavaFX has still lot of path to cover in
terms of popularity and usability of Swing. In Investment banking, where Java
rules on server side application development, Swing was heavily used in GUI
development couple of years back. Now trends is shifting towards C# for GUI
development due to couple of reasons e.g. good Swing developers are not easy to
be found as compared to C# developers. By the way there are still many
development work is going on Swing. One of the reason Swing developers are high
in demand is because Swing is quickly becoming a niche technology. This is
surprising because Swing is part of
Java, but given steep learning curve of Swing to master different layouts and
components e.g. JTable or JList , I tend
to believe it. In this article we will see some good Swing Interview questions
for practice. Questions like InvokeLater
vs InvokeAndWait are classic, which is always worth preparing.
Swing and AWT Interview Questions Answers
Here is my list of 10 useful Swing and AWT Interview questions in Java. As per my experience, Swing interview questions comes mainly from three parts : Swing API, Swing thread-safety issues and questions related to layout managers.
Question
1: What is EDT thread in Swing?
Answer : This is one of the basic questions in Swing and AWT interviews.
EDT stands for Event dispatcher thread. EDT is one of the most important thing
to learn about Swing, Since Swing is single-threaded all GUI drawing and event
handling is done in EDT thread and that's why its recommended not to perform
any time consuming task e.g. connecting
to database or opening network connection in Event Dispatcher
thread or EDT thread. If you do that, it may lead to frozen or hung GUI. This
question leads to several other questions in Java, e.g. If you can not open
database connection in EDT thread than how will you open db connection with
button click etc. well this can be done by spawning a new thread from button
click and opening db connection there.
Question
2: What is difference between invokeAndWait and invokeLater in Java?
Answer : This is one of my favourite Swing question in Java Interviews.
Knowledge of invokeAndWait and invokeLater is must for a
good Swing developer because Swing is not thread-safe
and at same time you can not perform time consuming task in EDT thread, as
discussed in first Swing interview question. InvokeAndWait and InvokeLater
method allows to enqueue task for EDT thread to perform, InvokeAndWait is a blocking
method in Java and does it synchronously and invokeLater does it
asynchronously. Since GUI can only be updated in Event dispatcher thread, if
you need to show progress of any task, you can use these two methods. See my
post Difference
between invokeAndWait and invokeLater in Java for more detailed answer of
this Swing question.
Question
3: What is difference between Swing and AWT in Java
Answer : One of the most frequently asked AWT and Swing Interview
question. One answer of this question is that, Swing is a considered as light
weight and AWT is considered as heavy weight. Another difference between AWT and Swing is that,
Swing offers uniform look and feel across platform while look and feel of AWT
GUI application are platform dependent because AWT mostly use native components
e.g. a AWT windows will look different in DOS and Windows operating system.
Question
4: What is difference between paint and repaint in Java Swing?
Answer : This can be a tough
Java question if you are not familiar with Swing API. Well, this is similar
to start() and run()
method of thread class. As calling start() method
will eventually calls run() method of Runnable
interface, Calling repaint() will call paint() method in
Swing. Since painting can only be done in EDT thread, repaint() just put a
paint request in EDT Queue, later EDT thread may combine several repaint
request to one and can perform repainting. repaint() is a not a
blocking method in Java and returns quickly.
Question
5: What is difference between BorderLayout and GridLayout ?
Answer : This is one of interesting Swing
interview question. BorderLayout and GridLayout are two
widely used LayoutManager from Swing API, former arranges
components in predefined position e.g. NORTH, SOUTH, EAST and
WEST while later arranges components one after other until there is space and
wraps them afterwards. This Swing question becomes more difficult when
Interviewer asked to write code to implement a layout e.g. drawing a layout and
ask you to implement as discussed in Top 10
Swing interview questions in Java.
Question
6: How to change a button from enable to disable after click ?
Answer : When button is clicked an action event is fired which can be
captured by implementing ActionListener interface and actionPerformed(ActionEvent
ae) method. You can then call button.setEnable(false) to disable
this button.
Question
7: Why Swing is called light weight ?
Answer : Most of Swing component
are inherited form JComponent and doesn't required a native peer
and that's why they are referred as light weight component. light weight
component implement look and feel in Java rather than using look and feel of
native component and that's why Swing's look and feel remains same across
platform.
Question
8: Is Swing Thread safe in Java ?
Answer : This is one of the tricky
question in Java Swing and AWT. No, Swing is not thread-safe in Java. Swing
components are not thread-safe they can not be modified from multiple threads.
All swing components are designed to be updated by using Event dispatcher
thread or EDT thread. See How
to write thread-safe code in Java to know more about thread-safety. By the way you can use invokeAndWait and invokeLater to safely
update swing components as discussed in previous Swing interview question.
Question
9: Which method of Swing are thread-safe?
Answer : This AWT and Swing question is asked as follow-up of previous
Swing interview question. Only couple of methods like repaint() and revalidate() are
thread-safe in Swing, i.e. they can be called from multiple threads without
additional synchronization
in Java.
Question
10: What is difference between Container and Component ?
Answer : Main difference between Container and Component is that
former can hold other components e.g. JFrame which is
used as container to hold other components e.g. JButton. This is
rather a simple Swing question and mostly asked in telephonic or upto 2 years
experienced programmers.
That's on this list of Swing Interview questions and answers in Java.
Despite reducing popularity and losing competition with C#, Swing is a
great GUI technology and one of the most preferred technology for implementing thick clients in Java.
Especially in finance and insurance domain, where client application need to
work with high volume of data, Java Swing is the solution. Good Swing
developers are hard to find and that's why well paid in this industry.
Other Java Interview Questions from Java67 Blog
Do they still ask AWT questions in Interview ? I thought Swing and AWT as old technologies, surprise to see it's still used.
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