AWT components are heavy-weight, whereas Swing components are lightweight. Hence Swing works faster than AWT. Heavy weight components depend on the local windowing toolkit. For example, java. awt. Button is a heavy weight component. Pluggable look and feel possible using java Swing. We can also change the look and feel of a Swing app while it’s running, which is not possible with AWT.
You can make a component handle its own events by giving it the event-listener interface it needs and adding itself as an event listener.
The paint() method supports painting via a Graphics object. The repaint() method is used to cause paint() to be invoked by the AWT painting thread.
javax. Swing package contains light weight components. All components in Swing, except JApplet, JDialog, JFrame and JWindow are lightweight components.
Containers hold and arrange other parts, even other containers, with the help of layout managers. These managers use layout policies to figure out where parts should go based on the size of the container.
What is a layout manager and what are different types of layout managers available in java Swing?
A layout manager is an object that is used to organize components in a container. The different layouts available are FlowLayout, BorderLayout, CardLayout, GridLayout and GridBagLayout.
FlowLayout: The elements of a FlowLayout are organized in a top to bottom, left to right fashion.
BorderLayout: The parts of a BorderLayout are arranged along the four sides (North, South, East, and West) and in the middle of a container.
CardLayout: The elements of a CardLayout are stacked, on top of the other, like a deck of cards.
GridLayout: The parts of a GridLayout are all the same size and are arranged in a square shape like a grid.
GridBagLayout: The elements of a GridBagLayout are organized according to a grid. Things could be different sizes, though, and they could take up more than one row or column of the grid. In addition, the rows and columns may have different sizes.
Java uses layout managers to lay out components in a consistent manner across all windowing platforms. Because Java’s layout managers aren’t limited to exact sizes and positions, they can work with differences in how windowing systems are set up.
The setLayout() method is used to specify a container’s layout. For example, setLayout(new FlowLayout()); will be set the layout as FlowLayout.
The enableEvents() method is used to enable an event for a particular component. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.
The Frame class extends Window to define a main application window that can have a menu bar.
Heavy weight components like Abstract Window Toolkit (AWT) depend on the local windowing toolkit. For example, java. awt . Button is a heavy weight component.
A Scrollbar is just a Component, but not a Container. A ScrollPane is a Container. A ScrollPane handles its own events and performs its own scrolling.
The preferred size of a component is the smallest size that will still let it show up without any problems.
Java Swing is a powerful and flexible GUI toolkit that lets developers make user interfaces that are rich and interactive. If you want to do well as a Java developer, you need to understand Swing and be able to answer common interview questions. This guide will go over 10 important Java Swing interview questions and give you full answers to help you ace your next interview.
1. What is the Event-Dispatcher-Thread (EDT) in Swing?
The Event-Dispatcher-Thread (EDT) is a special thread in Swing and AWT responsible for rendering graphics and handling events. It’s the central thread that manages all UI interactions and updates. It’s important to remember that time-consuming operations like database connections, file operations, or network requests should not be performed on the EDT as they can block the UI and lead to a frozen or unresponsive application. Instead, these tasks should be executed on separate threads, and the EDT can be used to spawn these threads upon user actions like button clicks or mouse events.
2 Is Swing thread-safe? Explain
Swing components are not thread-safe by default, which means that they can’t be changed from threads other than the EDT. If you try to do that, strange things might happen, like the GUI freezing up or showing wrong values. The Swing API has some methods that are safe to call from any thread, like repaint() and revalidate(). For other operations, it’s crucial to use techniques like SwingUtilities. invokeLater() or SwingUtilities. invokeAndWait() to safely update Swing components from non-EDT threads.
3. What are the key differences between Swing and AWT?
Here’s a breakdown of the key differences between Swing and AWT
- Component weight: AWT components are considered heavyweight, meaning they are directly mapped to native operating system components and consume more resources. Swing components, on the other hand, are lightweight and utilize the screen resources of their ancestor components, making them more efficient.
- Look and feel: Swing offers a pluggable look and feel, allowing developers to easily change the appearance of the entire application without modifying the underlying code. AWT, however, relies on native components, resulting in different appearances on different platforms.
- Platform independence: Swing components are written in Java and are platform-independent, ensuring consistent appearance and behavior across different operating systems. AWT components, being tied to native components, can exhibit platform-specific variations.
4. Why are Swing components called lightweight components?
As mentioned earlier, Swing components are called lightweight because they don’t directly interact with native operating system components. Instead, they utilize the screen resources of their ancestor components, making them more efficient and reducing resource consumption. This approach also contributes to platform independence, as the appearance is controlled by the Java code rather than native components.
5 Explain the difference between invokeLater() and invokeAndWait() methods in Swing
Both invokeLater() and invokeLater() are used to safely update Swing components from non-EDT threads. However, they differ in their execution behavior
invokeLater(): This method schedules the provided Runnable task to be executed on the EDT at a later time. It returns immediately without waiting for the task to complete.invokeAndWait(): This method also schedules the Runnable task on the EDT but waits for the task to finish before returning. This can be useful when the result of the task is needed in the current thread.
Choosing between these methods depends on the specific use case. If the task doesn’t require immediate results invokeLater() is preferred for its non-blocking nature. If the result is needed, invokeAndWait() is the appropriate choice.
6. Write code for a JTable with custom cell editor and custom cell renderer.
Custom cell editor:
import javax.swing.*;import javax.swing.table.*;public class CustomCellEditor extends AbstractCellEditor implements TableCellEditor { // ... implementation details for custom cell editor}Custom cell renderer:
import javax.swing.*;import javax.swing.table.*;public class CustomCellRenderer extends DefaultTableCellRenderer { // ... implementation details for custom cell renderer}7. How do you handle database, file, or network connections on a button click?
When dealing with database, file, or network operations triggered by button clicks, it’s crucial to avoid performing these tasks on the EDT to prevent UI freezes. The recommended approach is to create a separate thread to handle these operations. Here’s an example using an ActionListener:
button.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { // Disable the button to prevent multiple clicks button.setEnabled(false); // Create a new thread for the operation new Thread(() -> { // Perform the database/file/network operation // ... // Re-enable the button on the EDT after completion SwingUtilities.invokeLater(() -> button.setEnabled(true)); }).start(); }});8. Write code to print a layout using GridBagLayout.
import javax.swing.*;import java.awt.*;public class GridBagLayoutExample { public static void main(String[] args) { JFrame frame = new JFrame("GridBagLayout Example"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JPanel panel = new JPanel(new GridBagLayout()); // Create components and constraints JButton button1 = new JButton("Button 1"); JButton button2 = new JButton("Button 2"); JTextField textField = new JTextField(10); GridBagConstraints c = new GridBagConstraints(); // Add components to the panel with constraints c.gridx = 0; c.gridy = 0; panel.add(button1, c); c.gridx = 1; c.gridy = 0; panel.add(button2, c); c.gridx = 0; c.gridy = 1; c.gridwidth = 2; // Span two columns panel.add(textField, c); frame.add(panel); frame.pack(); frame.setVisible(true); }}9. Predict the output of the following code:
import javax.swing.*;public class CodeOutputPrediction { public static void main(String[] args) { JFrame frame = new JFrame("Output Prediction"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // Add components and layout here frame.pack(); frame.setVisible(true); }}10. Create a JList component that displays assets like Stocks, Futures, Options, and FX, sorted in ascending order, with assets starting with “Electronic trading” at the top.
import javax.swing.*;import java.util.Arrays;import java.util.Comparator;public class CustomJList { public static void main(String[] args) { String[] assets = {"Stocks", "Futures", "Options", "FX", "Electronic trading Stocks", "Electronic trading Futures"}; // Sort assets with custom comparator Arrays.sort(assets, new Comparator<String>() { @Override public int compare(String s1, String s2) { if (s1.startsWith("Electronic trading") && !s2.startsWith("Electronic trading")) { return -1; } else if (!s1.startsWith("Electronic trading") && s2.startsWith("Electronic trading")) { return 1; } else { return s1.compareTo(s2); } } }); // Create JList with custom model JList<String> list = new JList<>(assets); list.setModel(new AbstractListModel<String>() { @Override public int getSize() { return assets.length; } @Override public String getElementAt(int index) { return assets[index]; } }); // Create and display the frame JFrame frame = new JFrame("Custom JList"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.add(new JScrollPane(list)); frame.pack(); frame.setVisible(true); }}Mastering these 10 Java Swing interview questions will not only enhance your understanding of the framework but also demonstrate your ability to solve practical problems using Swing concepts. By practicing these concepts and applying them to real-world scenarios, you’ll be well-equipped to tackle any Swing-related challenges you might encounter in your development journey.
C H A P T E R S Java Interview Questions
What is the difference between Swing and AWT components?
AWT components are heavy-weight, whereas Swing components are lightweight. Hence Swing works faster than AWT. Heavy weight components depend on the local windowing toolkit. For example, java. awt. Button is a heavy weight component. Pluggable look and feel possible using java Swing. We can also change the look and feel of a Swing app while it’s running, which is not possible with AWT.
Name the containers which use Border Layout as their default layout?
window, Frame and Dialog classes.
Name Container classes.
Window, Frame, Dialog, FileDialog, Panel, Applet, or ScrollPane
How can a GUI component handle its own events?
You can make a component handle its own events by giving it the event-listener interface it needs and adding itself as an event listener.
What is the difference between the paint() and repaint() methods?
The paint() method supports painting via a Graphics object. The repaint() method is used to cause paint() to be invoked by the AWT painting thread.
Which package has light weight components?
javax. Swing package contains light weight components. All components in Swing, except JApplet, JDialog, JFrame and JWindow are lightweight components.
What are peerless components?
The peerless components are called light weight components.
What is a Container in a GUI?
Containers hold and arrange other parts, even other containers, with the help of layout managers. These managers use layout policies to figure out where parts should go based on the size of the container.
How are the elements of a GridBagLayout organized?
Or
What is a layout manager and what are different types of layout managers available in java Swing?
Or
How are the elements of different layouts organized?
A layout manager is an object that is used to organize components in a container. The different layouts available are FlowLayout, BorderLayout, CardLayout, GridLayout and GridBagLayout.
FlowLayout: The elements of a FlowLayout are organized in a top to bottom, left to right fashion.
BorderLayout: The parts of a BorderLayout are arranged along the four sides (North, South, East, and West) and in the middle of a container.
CardLayout: The elements of a CardLayout are stacked, on top of the other, like a deck of cards.
GridLayout: The parts of a GridLayout are all the same size and are arranged in a square shape like a grid.
GridBagLayout: The elements of a GridBagLayout are organized according to a grid. Things could be different sizes, though, and they could take up more than one row or column of the grid. In addition, the rows and columns may have different sizes.
What advantage do Java’s layout managers provide over traditional windowing systems?
Java uses layout managers to lay out components in a consistent manner across all windowing platforms. Because Java’s layout managers aren’t limited to exact sizes and positions, they can work with differences in how windowing systems are set up.
What method is used to specify a container’s layout?
The setLayout() method is used to specify a container’s layout. For example, setLayout(new FlowLayout()); will be set the layout as FlowLayout.
Which Container method is used to cause a container to be laid out and redisplayed?
Name Component subclasses that support painting.
The Canvas, Frame, Panel, and Applet classes support painting.
What is the purpose of the enableEvents() method?
The enableEvents() method is used to enable an event for a particular component. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.
What is the difference between a Window and a Frame?
The Frame class extends Window to define a main application window that can have a menu bar.
What do heavy weight components mean?
Heavy weight components like Abstract Window Toolkit (AWT) depend on the local windowing toolkit. For example, java. awt . Button is a heavy weight component.
What is the difference between a Scrollbar and a ScrollPane?
A Scrollbar is just a Component, but not a Container. A ScrollPane is a Container. A ScrollPane handles its own events and performs its own scrolling.
What is the preferred size of a component?
The preferred size of a component is the smallest size that will still let it show up without any problems.
Which containers use a FlowLayout as their default layout?
The Panel and Applet classes use the FlowLayout as their default layout.
Java awt and swing interview questions
FAQ
What is Java Swing used for?
What is the framework of Java Swing?
What are the two key features of Swing in Java?
What are the capabilities of Java Swing?
