Question

Which class fires ActionEvent at periodic intervals? a. JButton b. JMenu c. swing. Timer d. util.Timer e. None of the above

Short answer

c. swing.Timer

Step-by-step solution

Understand ActionEvents

ActionEvents are events generated by components like buttons and timers in response to some user interaction or a predefined condition, like a timer reaching zero.

Identify the options

Analyze each option given. We need to find out which one fires ActionEvent at periodic intervals.

Evaluate JButton

A JButton generates ActionEvents when it is clicked by the user. It does not, however, fire events at periodic intervals, so this option can be ruled out.

Evaluate JMenu

A JMenu also generates ActionEvents when a menu item is selected by the user. It does not fire events at periodic intervals, so this option is also incorrect.

Evaluate swing.Timer

The swing.Timer class in Java is used to fire ActionEvents at regular intervals. It is often used to perform an action periodically, like updating a clock.

Evaluate util.Timer

The util.Timer class is used to schedule tasks for future execution in a background thread. It does not fire ActionEvents but instead schedules TimerTasks.

Conclude

By evaluating the options, we see that only the swing.Timer class fires ActionEvents at periodic intervals.

Key concepts

Swing Timer

The swing.Timer class in Java is a tool that can be used to perform actions periodically. It fires ActionEvents at predefined intervals, which can be highly useful for tasks like creating animations, games, or updating clocks.

• To create a Timer, you can use the constructor new Timer(int delay, ActionListener listener).
• The delay parameter defines the interval in milliseconds between action events.
• The ActionListener is a callback interface that gets called each time the event fires.

Here is a basic example:
Timer timer = new Timer(1000, new ActionListener() {
public void actionPerformed(ActionEvent e) {
// code to run periodically
}
});
timer.start();
In this example, the timer will call actionPerformed every 1000 milliseconds (1 second). The Timer is especially useful in Swing applications to ensure that the GUI remains responsive while performing periodic tasks.

JButton

A JButton is a GUI component that can trigger actions when clicked by the user. It is part of the Java Swing library and provides an interactive element for users to interact with.

• To create a JButton, you can use the constructor new JButton(String text).
• You can add an ActionListener to the JButton to define what happens when it is clicked.

Here is a basic example of creating a JButton and adding an ActionListener:
JButton button = new JButton('Click Me');
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
// code to execute when button is clicked
}
});
The above code will trigger the actionPerformed method every time the JButton is clicked by the user. Note that, unlike swing.Timer, JButton does not fire ActionEvents at periodic intervals but instead in response to user actions.

JMenu

A JMenu is another key component in the Swing library, typically used for creating dropdown menus in an application's menu bar.

• Like JButton, JMenu can generate ActionEvents, mostly when a menu item is selected.
• It is part of the overall GUI structure and enhances user interaction by providing multiple choices in a structured format.

Here is how you can create a JMenu with menu items:
JMenu menu = new JMenu('File');
JMenuItem openItem = new JMenuItem('Open');
menu.add(openItem);
openItem.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
// code to execute when 'Open' is selected
}
});
This setup adds an 'Open' menu item to the 'File' menu. Each time 'Open' is selected, the associated actionPerformed method is called. Unlike swing.Timer, the JButton and JMenu do not fire events periodically. Instead, they respond to user interactions, making them essential for creating interactive applications.