1. Tonga Institute of Higher Education
Event Handling
Tonga Institute of Higher Education

2. Event Driven Programs
Event Driven Programs – The program responds to a user event
Event - An action or occurrence detected by a program
User
Clicking a mouse button
Pressing a key
System
Running out of memory
An error occurring
For example, your program might work like this:
Show a form with a welcome message. The form will also contain a textbox, OK button and instructions to enter their name and click the Ok button.
Wait for the user to respond
When the user performs an action,
If the user clicks the X in the top right corner, quit the program
If the user typed in their name and pressed the OK button, show a message that you are happy to meet them
Gives more freedom to the user. It reacts to the user’s actions
Gives user the impression that they are in control
Frames are event driven!

3. Current Situation We learned how to display a graphical user interface
However, it doesn’t do anything
Event – Something that is triggered by the user of a GUI
Listener – Code that can detect and respond to events
Register – To associate a listener with a GUI object

4. Button Listener Class Need to import packages Need to make a class
To handle events. Don’t forget
to implement ActionListener!
Handles
2 buttons
This is the
text of the
button that
will be handled
The only code you should change has
a yellow background

5. Setting Up Button Listeners
Declare and Initialize
the Listeners
Same listener
Must use
this method
Register the Listeners
(Connect the listener
to the button)

6. Demonstration
GUI

7. Button Listener Class that Accepts a Frame
This listener keeps track of the
frame so it can change the frame.
Pass in the frame through
the constructor
This changes the
text for the button
on the frame.
The only code you should change has
a yellow background

8. Setting Up Listeners that Passes a Frame
Declare and Initialize
the Listeners
Pass this
frame in the
constructor
Register the Listeners
(Connect the listener
to the button)

9. Demonstration
GUI2

10. Frame Listener Class Only change code that is inside of the brackets
Everything else
should be the same!

11. Setting up a Form Listener
This is the
constructor
Use the word
this to add a
listener
Same listener

12. Demonstration
GUI3