Java Event Handling Lecture Notes

Introduction

• Java offers many supports for programmers, including the AWT package.
• AWT package aids in developing window programs conveniently.
• Today's focus: Event Handling in Java.
  • Essential for window-based program development.

Concept of Event

• An event occurs during program execution, often through user interactions.
• Examples:
  • Typing or pressing a key.
  • Clicking a button with a mouse.
• Events require a response or action from the system.

Types of Events

• Foreground Events: Related to graphical user interface (GUI).
• Background Events: Occur at the operating system level (e.g., pressing restart).

Event Sources in GUI

• Components like buttons, checkboxes, choices, etc.
• Events are generated from these components.
• Event types include:
  • Action Event: From buttons or lists.
  • Item Event: From checkboxes or choices.
  • Adjustment Event: From scroll bars.
  • Text Event: From text fields.
  • Key Event and Mouse Event: From keyboard and mouse interactions.

Event Handling in Java

• Events are managed using software mechanisms in Java, particularly within GUI contexts.
• AWT Event Classes and Interfaces:
  • Classes such as ActionEvent, ComponentEvent, MouseEvent, etc.
  • Interfaces like ActionListener, ItemListener, KeyListener, etc.

Event Handling Process

1. Event Creation: Triggered by user interaction, generates an event object.
2. Listener Registration: Listeners are registered to handle events.
3. Listener Implementation: Define actions in response to events.

Examples of Event Handling

• Mouse Event Handling: Implement MouseListener and MouseMotionListener.
  • Register listeners using methods like addMouseListener().
  • Implement methods such as mousePressed(), mouseDragged().
• Keyboard Event Handling: Implement KeyListener.
  • Register using addKeyListener() and requestFocus().
  • Implement methods like keyPressed(), keyReleased(), keyTyped().

Summary

• Understand event handling components: events, listeners, and methods.
• Only two steps in event handling: Register listeners and implement listener methods.
• Examples focus on mouse and keyboard events due to time constraints.

Further Learning

• Review Java documentation and additional resources for depth in event handling.
• Practical examples aid in understanding event handling mechanics.