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Questions and Answers
In the event delegation model, what role does the 'Source' play?
In the event delegation model, what role does the 'Source' play?
- It is the component that triggers an event. (correct)
- It manages the flow of events between listeners.
- It processes the event and determines the response.
- It encapsulates information about the event.
What information is contained within an 'Event Object'?
What information is contained within an 'Event Object'?
- The component that will handle the event.
- Details about what specific event occurred. (correct)
- The layout of the GUI components.
- The methods to handle the event.
What is the primary responsibility of an 'Event Listener'?
What is the primary responsibility of an 'Event Listener'?
- To manage the layout of the application.
- To define the appearance of the components.
- To detect events and determine the appropriate response. (correct)
- To create the GUI components.
If a user clicks a button in a Java Swing application, which type of Event Object is typically created?
If a user clicks a button in a Java Swing application, which type of Event Object is typically created?
Which interface is commonly used to handle button click events in Java Swing?
Which interface is commonly used to handle button click events in Java Swing?
What is the correct sequence of steps for event handling in Java?
What is the correct sequence of steps for event handling in Java?
In NetBeans, which action allows you to auto-generate the event handling method for a button click?
In NetBeans, which action allows you to auto-generate the event handling method for a button click?
What is the purpose of the initComponents() method in a NetBeans-generated Swing form?
What is the purpose of the initComponents() method in a NetBeans-generated Swing form?
Which of the following steps is NOT typically part of implementing event handling in Java?
Which of the following steps is NOT typically part of implementing event handling in Java?
When creating a Swing application in NetBeans, where do you typically add components to the form?
When creating a Swing application in NetBeans, where do you typically add components to the form?
What is a Swing Applet?
What is a Swing Applet?
Which method is typically overridden in a Swing Applet to initialize the applet's components and behavior?
Which method is typically overridden in a Swing Applet to initialize the applet's components and behavior?
Why are Java Applets largely deprecated?
Why are Java Applets largely deprecated?
Which class should a Swing Applet extend?
Which class should a Swing Applet extend?
In a Swing Applet, how can you set the position and size of components without using a layout manager?
In a Swing Applet, how can you set the position and size of components without using a layout manager?
Which of the following is the correct way to add an ActionListener to a JButton in Java?
Which of the following is the correct way to add an ActionListener to a JButton in Java?
Suppose you have a JTextField named inputField, and you want to retrieve the text entered by the user. Which method should you use?
Suppose you have a JTextField named inputField, and you want to retrieve the text entered by the user. Which method should you use?
Which layout manager is commonly used when you need to specify the exact size and position of each component in a container?
Which layout manager is commonly used when you need to specify the exact size and position of each component in a container?
In the context of event handling, what does it mean to 'implement a listener interface'?
In the context of event handling, what does it mean to 'implement a listener interface'?
What is the primary reason to use the Event Delegation Model in Java?
What is the primary reason to use the Event Delegation Model in Java?
In a basic Swing calculator application, which component is most suitable for displaying the input and results?
In a basic Swing calculator application, which component is most suitable for displaying the input and results?
Which code snippet correctly adds a button to a JApplet and sets its position and size?
Which code snippet correctly adds a button to a JApplet and sets its position and size?
How do you typically handle multiple button clicks in a Swing application so that each button performs a different action?
How do you typically handle multiple button clicks in a Swing application so that each button performs a different action?
In Java Swing, what is the purpose of the pack() method?
In Java Swing, what is the purpose of the pack() method?
Which of the following is the correct way to set the text of a JLabel named messageLabel in Java?
Which of the following is the correct way to set the text of a JLabel named messageLabel in Java?
What is the main advantage of using a layout manager in Swing?
What is the main advantage of using a layout manager in Swing?
When you create a custom event handler in Java, what must you do to ensure it responds to a specific event?
When you create a custom event handler in Java, what must you do to ensure it responds to a specific event?
What is the purpose of the @SuppressWarnings("unchecked") annotation in Java code?
What is the purpose of the @SuppressWarnings("unchecked") annotation in Java code?
Which of the following is NOT a standard method in the java.awt.Component class?
Which of the following is NOT a standard method in the java.awt.Component class?
Flashcards
Event Handling
Event Handling
Responding to user actions in a Java program, like clicks or typing.
Event Source
Event Source
The GUI component that triggers an event.
Event Object
Event Object
Carries information about an event that occurred, like a button click or key press.
Event Listener
Event Listener
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ActionListener
ActionListener
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MouseListener
MouseListener
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KeyListener
KeyListener
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Swing Applet
Swing Applet
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init() Method
init() Method
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Study Notes
Introduction to Event Handling in Swing
- Event handling is essential for creating interactive Java programs.
- It allows programs to respond to user actions like clicks, typing, and mouse movements.
- Swing, a Java GUI toolkit, uses event handling.
The Event Delegation Model
- Java uses the event delegation model to manage user actions.
- Key parts include the Source, Event Object, and Event Listener.
Source
- This is the component that triggers an event.
- Example: A JButton that is clicked.
Event Object
- It is created when an event occurs.
- It holds information about the event.
- Example: ActionEvent for a button click, MouseEvent for mouse movement.
Event Listener
- It listens for specific events and tells the program how to respond.
- Example: ActionListener listens for button clicks.
How Event Handling Works
- A source (e.g., a button) is clicked.
- An event object is created (e.g., ActionEvent).
- The event listener attached to the button "hears" the event.
- The event listener performs an action in response (e.g., changes text, shows a message).
Example of Event Handling in Action
- A button click triggers a label to display "Button Clicked!".
- The button is the source.
- An ActionEvent is created.
- An ActionListener updates the label text.
Event Delegation Model Participants
- The Event Source is the GUI component that triggers the event such as a JButton or JTextField.
- The Event Object encapsulates information about the event; specific classes for different event types like ActionEvent, KeyEvent, and MouseEvent are included.
- The Event Listener is an interface that processes the event, linked to a component to "listen" for specific events.
- Common Event Listener Interfaces:
- ActionListener handles action events (e.g., button clicks).
- MouseListener handles mouse events (e.g., clicks, movement).
- KeyListener handles keyboard input events.
Implementing Event Handling
- Register the component with an event listener.
- Implement the listener interface by overriding the required methods.
- Perform actions inside the event handler when the event occurs.
Example 1: Handling Button Click Events in NetBeans
- Create a new Java Application Project: File > New Project > Java Application.
- Create a Swing Form: New > JFrame Form.
- Design the GUI by dragging and dropping a JLabel and a JButton.
- Add an Event Listener to the Button: Events > Action > actionPerformed.
- Write code inside the actionPerformed() method to update the JLabel text.
Swing Applets
- A Swing Applet is a Java application that runs in a web browser or an applet viewer.
- They are now largely deprecated due to security concerns.
- Applets extend javax.swing.JApplet (or java.applet.Applet for AWT).
- They override the init() method to initialize the applet.
Example 2: A Simple Swing Applet in NetBeans
- Create a New Java Class.
- Write the Applet Code, initializing the applet with a button and a label.
- Set the layout and add components, then add an event listener to the button.
- To run the applet in NetBeans, you’ll need an applet viewer since browsers no longer support applets.
Exercises for Week 2
- Objective is to create a Java Swing application with multiple buttons; each button should update a different label with a different message
- Add three JButton components to your form.
- Add three JLabel components.
- Write event handling code for each button to update the text of a different label when clicked.
- Objective is to develop a basic Swing calculator with buttons for digits (0-9), addition, subtraction, and equals.
- Create a form with JButton components for the numbers and operations.
- Add a JTextField to display the result.
- Implement event handling so that clicking on a number or operator updates the result in the text field.
- Objective is to Develop a Swing applet that includes two buttons and a label; each button click should update the label with a different message.
- Create a JApplet class and override the init() method.
- Add two buttons and one label to the applet.
- Implement event handling for each button to change the label text.
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