Java Swing Interview Questions and Answers

Java Swing exists as a segment of Java Foundation Classes (JFC), which delivers a comprehensive set of GUI elements to construct Java desktop applications. Swing offers improved visual features in addition to being lightweight and independent from platform restrictions when compared to AWT (Abstract Window Toolkit).

The following piece covers 15 essential questions for Java Swing interviews, together with complete code illustrations and clear explanations.

1. What is Java Swing?

The Java Swing toolkit serves as a Java mechanism that enables programmers to build window-based applications. AWT received an upgrade through Java Swing, which delivered minimally weighted user interface elements that operate across multiple platforms.

Key Features of Swing

• Part of Java Foundation Classes (JFC)
• Uses lightweight components (not dependent on the OS)
• Supports Model-View-Controller (MVC) architecture
• Provides pluggable Look & Feel

2. What is the MVC architecture in Swing?

Supporting Model-View-Controller (MVC) architecture divides operations into Model-View-Controller parts in Swing applications:

Model: Manages data & logic

View: Renders UI elements

Controller: Handles interactions between UI & logic

For example, in JTable:

• TableModel is the Model.
• JTable is the View.
• TableCellRenderer is the Controller.

The design of this architecture leads to improved system components along with higher reuse potential.

3. Orbital makes two categories of components: heavyweights and lightweights. What does this distinction mean?

Heavyweight Components: It depends on native OS components (for example, Button, Frame in AWT).

Lightweight Components: It is drawn by Java, making it faster and more flexible (for example, JButton, JFrame).

Swing components operate with reduced weight to enhance their compatibility across different platforms.

4. What is the difference between paint() and paintComponent() method?

paint(): It is used in AWT for heavyweight components.

paintComponent(): It is used in Swing, allowing custom painting efficiently.

When customising Swing components, always override paintComponent():

5. What are the differences between Swing and AWT?

Java Swing is a part of Java Foundation Classes (JFC) that is used to create window-based applications. It is built on the top of AWT (Abstract Windowing Toolkit) API and entirely written in Java.

Java Swing provides better lightweight components than AWT. The javax.swing package provides classes for Java Swing components such as JButton, JTextField, JTextArea, JRadioButton, JCheckbox, JMenu, JColorChooser etc.

6. How do you create a simple Swing application?

Here’s a basic Swing application:

A new window containing a button appears due to the instruction.

7. What is SwingUtilities.invokeLater()?

The lack of thread safety in Swing forces users to update the user interface on the Event Dispatch Thread (EDT) through the following method:

It prevents concurrency issues in GUI applications.

8. The purpose of this tool is to display tabular data within Swing applications.

When developing Swing applications JTable serves as the preferred component for showing tabular data presentation.

JTable implements MVC architecture to give users customisable options for flexibility.

9. How do you add a tooltip to a Swing component?

Use setToolTipText():

The system enhances user experience by offering practical tips to its users.

10. What is the purpose of JScrollPane?

The JScrollPane component enables users to scroll within large displays that contain JTextArea and JTable components.

11. What steps are needed to modify the appearance of a Swing application?

Use UIManager.setLookAndFeel():

This applies the OS-native look and feel to your application.

12. What is the use of the JTree component in Swing?

The JTree UI component serves as a hierarchical element to present tree structures, including file directories.

Custom user interface presentation and expandable node features exist within JTree Implementation.

13. How do you create a pop-up menu in Swing?

JPopupMenu provides the means to generate context menus that users open through right-click actions.

A right-click on the panel activates the pop-up menu.

14. How can you make a Swing application thread-safe?

Swing applications are not thread-safe by default. To make them thread-safe, we must ensure that all Swing component manipulations occur on the Event Dispatch Thread (EDT). It can be achieved by using methods like invokeLater() and invokeAndWait(), which queue tasks to be executed on the EDT.

For instance, if we want to update a JLabel’s text, instead of directly calling setText(), we should use:

It ensures that the label update happens on the EDT, preventing potential race conditions or other threading issues.

15. How do you create a non-blocking progress bar in Swing?

Assist real-time progress monitoring through the combination of JProgressBar along with SwingWorker.

Keeps the UI responsive while updating progress.

16. How do you create a non-modal JDialog?

Set setModal(false).

17. What is the purpose of setOpaque(false) in Swing?

Setting setOpaque(false) makes a component transparent.

18. What steps do you need to develop a Swing look and feel design from scratch?

Use UIManager.setLookAndFeel() method.

19. Is there a method to attach a keyboard command to a JButton?

The setMnemonic() method enables the allocation of shortcut key associations.

20. How do you make a JFrame always stay on top?

To make a JFrame always on top, we use the setAlwaysOnTop(true) method.