Lecture 4

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Questions and Answers

Which step is essential when enabling a class to respond to action events?

Implementing the `ItemListener` interface.
Overriding the `paintComponent()` method.
Extending the `JComponent` class.
Implementing the `ActionListener` interface. (correct)

What is the purpose of the `addActionListener()` method?

To create a new instance of an action event.
To register a component with the listener class, enabling it to respond to action events. (correct)
To specify the visual appearance of a component.
To define the layout of components within a container.

Which method must be overridden in a class that implements `ActionListener` to define the action to be performed when an event occurs?

`componentResized(ComponentEvent e)`
`mouseClicked(MouseEvent e)`
`keyPressed(KeyEvent e)`
`actionPerformed(ActionEvent e)` (correct)

In the `Beeper` class example, what is the purpose of the line `button.setPreferredSize(new Dimension(200, 80));`?

It defines the preferred size, width 200 and height 80, of the button. (D) Signup and view all the answers

What would happen if the line `button.addActionListener(this);` was removed from the `Beeper` class?

Clicking the button would have no effect. (B) Signup and view all the answers

Inside the `actionPerformed` method of the `Beeper` class, what does `Toolkit.getDefaultToolkit().beep();` do?

It produces a system beep sound. (C) Signup and view all the answers

What layout manager is being used in the `Beeper` class?

<code>BorderLayout</code> (D) Signup and view all the answers

In the `createAndShowGUI()` method, what is the purpose of `frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);`?

It terminates the application when the close button is pressed. (C) Signup and view all the answers

In the delegation event model, what is the primary role of the component from which an event originates?

To transmit the event to one or more registered listener classes. (C) Signup and view all the answers

Which of the following best describes the role of an event handler?

A method that receives an event object and reacts to the user’s action. (C) Signup and view all the answers

Which of the following is the most accurate definition of an 'event' in the context of event handling?

An object that contains information representing a state change in a source. (D) Signup and view all the answers

Consider a scenario where a user clicks a button in a GUI. Which component is considered the 'event source'?

The JButton component. (D) Signup and view all the answers

What is the primary benefit of using the delegation event model in GUI programming?

It allows multiple components to react to the same event independently. (C) Signup and view all the answers

What is the relationship between events, event sources, and event listeners in GUI programming?

Event sources generate events, which are then received and processed by event listeners. (A) Signup and view all the answers

An event is generated when a user interacts with a GUI element. Which of the following is contained in the event?

Information describing the interaction that occurred. (A) Signup and view all the answers

Which statement accurately describes the function of a listener in event-driven programming?

Listeners passively wait for specific events and then execute predefined actions. (C) Signup and view all the answers

Which of the following best describes the role of a listener in the Java delegation event model?

To receive, process, and handle events triggered by user interactions or system activities. (D) Signup and view all the answers

Suppose you have a custom GUI component that needs to respond to both mouse clicks and key presses. What is the most appropriate way to enable this functionality using the delegation event model?

Create separate listener classes that implement <code>MouseListener</code> and <code>KeyListener</code>, and register them with the component. (C) Signup and view all the answers

What is the primary difference between foreground and background events in the Java delegation event model?

Foreground events require direct user interaction, while background events result from system activities or indirect user actions. (D) Signup and view all the answers

What is the purpose of `invokeLater` in the provided code snippet?

To place the execution of <code>createAndShowGUI()</code> onto the event dispatch thread (EDT) to ensure GUI updates are thread-safe. (D) Signup and view all the answers

In the AWT Toolkit example, what does the line `Toolkit t = Toolkit.getDefaultToolkit();` achieve?

It retrieves the default toolkit for the system, allowing access to screen dimensions and resolution. (C) Signup and view all the answers

Which of the following code snippets correctly registers an `ActionListener` to a `JButton` instance named `myButton`?

<code>myButton.addActionListener(this);</code> (assuming 'this' implements ActionListener) (C) Signup and view all the answers

Consider a scenario where a `TextField` and a `TextArea` are both present in a GUI. You want to capture text changes in both components. Which listener interface(s) would be most suitable?

<code>TextListener</code> for both <code>TextField</code> and <code>TextArea</code> (D) Signup and view all the answers

How does JavaFX handle events compared to older Java versions?

JavaFX employs the same event delegation model but utilizes different API classes for implementation. (C) Signup and view all the answers

In JavaFX, what is the role of a controller class when handling button click events?

It implements the <code>EventHandler</code> interface to define the action to be performed when the button is clicked. (B) Signup and view all the answers

A `WindowListener` is attached to a `JFrame`. Which method is invoked when the user clicks the close button on the frame's title bar, initiating the window closing process?

<code>windowClosing()</code> (A) Signup and view all the answers

Which event is generated when a button is clicked in a Java Swing application, and which listener interface should be used to handle this event?

<code>ActionEvent</code>, handled by <code>ActionListener</code> (A) Signup and view all the answers

What is a potential drawback of using lambdas for event handling in larger JavaFX projects?

Lambdas can make the code harder to read and maintain in larger projects due to their compact and inline nature. (A) Signup and view all the answers

Analyze the provided JavaFX code snippet:

`btn.setOnAction(event -> System.out.println("Hello World!"));`

What does this code achieve?

It prints "Hello World!" to the console whenever the button is clicked. (A) Signup and view all the answers

In the context of the Java delegation event model, what does it mean for an event source to 'fire' an event?

To generate an event and notify all registered listeners about its occurrence. (C) Signup and view all the answers

Consider the following scenario: You have a complex JavaFX application with numerous buttons and event handlers. Which approach would generally be preferable for managing event handling and maintaining code readability?

Implementing separate controller classes that implement the <code>EventHandler</code> interface, with clearly defined <code>handle</code> methods for each event. (C) Signup and view all the answers

Suppose you want to retrieve the screen size in pixels. In what way is `java.awt.Toolkit` useful?

It provides methods to obtain the screen resolution and dimensions, such as width and height. (B) Signup and view all the answers

Flashcards

Events

Objects that contain information about what has happened in the application.

Event source

A generator (originator) of the event. For example, a JButton component.