Event Handling

Event Handling

1. What Is an Event? (beginner)

Event = user did something (clicked, typed, closed!). Handling = code runs in reply (button → bill!). Flow: source (button!) → event object (ActionEvent!) → listener (your code!).

Button (source!) --click--> ActionEvent (what/where!) --dispatch--> actionPerformed() (your reply!)

Three steps: implement → register (addXListener) → handle (callback!).

4. Traps

• Forgot addActionListener → click does NOTHING (most common!).
• Wrong method name (actionperformd) → no override (use @Override to catch!).
• Long work in handler freezes UI (use thread!).

5. Exam Points

• Counter program + 3 steps — 7 marks, very frequent.
• Delegation flow — 3-5 marks, frequent.