Event-Driven Programming and AWT

• Event-Driven Programming is a programming paradigm where the flow of the program is determined by events such as user actions (mouse clicks, key presses) or system-generated events.

Key Concepts in Event-Driven Programming

• Event: An occurrence triggered by user interaction or system activity (e.g., button click, mouse movement).
• Event Source: is the component that generates the event (e.g., JButton).
• Event Listener: An object that listens for events and responds accordingly (e.g., ActionListener).
• Callback Methods: Methods that execute when an event occurs.

Examples of Events

• Clicking a button.
• Moving the mouse.
• Typing on the keyboard.
• Closing or minimizing a window.

Why Event-Driven Programming?

• Essential for GUI applications to allow user interaction.
• Provides better user experience by responding dynamically to inputs.

AWT (Abstract Window Toolkit)

• A Java library used for creating GUI applications.
• Provides components like buttons, labels, text fields, and windows.
• Uses native OS components (heavyweight components).

AWT Components

• Frame: A window with a title bar (main application window).
• Label: Displays a single line of text.
• Button: A clickable button that performs an action.
• TextField: A single-line text input field.
• Panel: A generic container that holds other components.

AWT Containers

• Frame: Top-level container for holding GUI components.
• Panel: Used to group multiple components together.

AWT Event Handling

• Uses Listeners to capture and respond to user actions.
• Common Event Listeners:
  • ActionListener: Handles button clicks.
  • MouseListener: Handles mouse events (click, press, release, enter, exit).
  • KeyListener: Handles keyboard inputs.

Steps to Handle Events

• Implement the required listener interface.
• Register the listener with the event source.
• Override the appropriate method to define actions.

What is Swing?

• Swing is a GUI toolkit for Java, part of the Java.

Key Features of Swing

• Platform-independent: Provides a consistent look and feel across operating systems.
• Lightweight components: Do not rely on native OS components (rendered in Java).
• Highly customizable: Developers can change component appearance using Look and Feel (LAF).

Common Swing Components

• JFrame: Main application window.
• JPanel: A lightweight container used to group components.
• JLabel: Displays text or images.
• JButton: A clickable button to trigger an action.
• JTextField: A single-line text input field.
• JTextArea: A multi-line text input area.
• JCheckBox: Allows multiple selections from a list.
• JRadioButton: Allows only one selection in a group.
• JComboBox: A drop-down list for selecting an item.
• JList: Displays a list of selectable items.
• JTable: Used to display tabular data.
• JMenuBar, JMenu, JMenultem: Used to create application menus.
• JTree: Represents hierarchical data (e.g., file directory).
• JTabbedPane: Allows switching between panels using tabs.
• JSlider: Enables users to select a value from a range.
• JProgressBar: Displays the progress of a task visual.

Layout Managers in Java Swing

• A mechanism for positioning and sizing GUI components in a container to avoid manual positioning using absolute values.
• FlowLayout: Arranges components horizontally, wrapping if necessary.
• BorderLayout: Divides the container into five regions (NORTH, SOUTH, EAST, WEST, CENTER).
• GridLayout: Organizes components in a grid with equal-sized cells.
• Custom Layouts: Developers can implement their own layouts by overriding LayoutManager methods.
• BoxLayout: Arranges components vertically or horizontally.
• CardLayout: Stacks multiple components but shows only one at a time.

Event Handling in Java

• Mechanism that manages user interactions with GUI components.
• Events occur when users interact with buttons, text fields, checkboxes, etc.

Common Event Classes

• ActionEvent: Handles button clicks and menu selections.
• ItemEvent: Used for checkboxes, combo boxes, radio button selections.
• MouseEvent: Captures mouse clicks, movement, and hover actions.
• KeyEvent: Handles keyboard input detection.
• WindowEvent: Detects window interactions (open, close, minimize, maximize).

Examples of Events

• Clicking a button.
• Moving the mouse.
• Typing on the keyboard.
• Closing or minimizing a window.

Swing Dialogs

• A popup window used to display messages, gather input, or confirm user actions.
• Created using the JOptionPane class.
  • Message Dialog (showMessageDialog): Displays information, warnings, or errors with an ok button.
    • Example: JOptionPane.showMessageDialog(null, "Hello, User!");

Confirmation Dialog (showConfirmDialog)

• Asks the user to confirm an action with Yes/No/Cancel options.
  • Example: int choice = JOptionPane.showConfirmDialog(null, "Are you sure?", "Confirm", JOptionPane.YES_NO_OPTION);
    • If (choice == JOptionPane.YES_OPTION) { System.out.println("User clicked YES"); }

Input Dialog (showInputDialog)

• Displays a question and gets the user's input from the text field, combo box or list.
  • Example: String name = JOptionPane.showInputDialog("Enter your name:");

Option Dialog (showOptionDialog)

• Displays a question and gets the user's response from the set of customized options.

Other Swing Dialogs

• JColorChooser: Allows the user to select a color.
  • Example: Color color = JColorChooser.showDialog(null, "Choose a Color", Color.RED);
• JFileChooser: Opens a file selection dialog.
  • Example: JFileChooser fileChooser = new JFileChooser(); int returnValue = fileChooser.showOpenDialog(null); if (returnValue == JFileChooser.APPROVE_OPTION) { File selectedFile = fileChooser.getSelectedFile(); System.out.println("Selected file: " + selectedFile.getAbsolutePath()); }
  • parentComponent: Determines which JFrame will be the parent of the dialog box. Can be any component or null. If null, the dialog appears in the center of the screen.
  • message: The content to be displayed inside the dialog box. Can be any object, but typically a String is used. Example: "This is a message dialog!". NOTE: The message dialog will work as long as the parentComponent and message parameters are supplied.
  • title: The text displayed in the title bar of the dialog. Default value is "Message". Example: "Warning" or "Error".
  • messageType: Specifies the type of message the dialog will display. Can be a number or a constant value from JOptionPane. Determines the icon shown in the dialog.
    • PLAIN_MESSAGE (-1): Displays a message with no icon.
    • ERROR_MESSAGE (0): Displays an error icon indicating a program error.
    • INFORMATION_MESSAGE (1): Displays an information icon for informational messages.
    • WARNING_MESSAGE (2): Displays a warning icon for potential issues.
    • QUESTION_MESSAGE (3): Displays a question icon, usually requiring a user response.
  • icon: The custom icon to display in the message dialog, which can be specified using the ImageIcon class with supported formats: JPEG, PNG, GIF.