1. Ellen Walker Hiram College
Java GUI Programming 1
Ellen Walker
Hiram College

2. What is a GUI? Graphical User Interface
Easier (for most people) to use
More complex to program

3. Why Java? Java compiles for a virtual machine
“Write once run anywhere”
One program looks nice on:
Linux
Windows
Macintosh
Can also generate “applets” to run from Web pages (not today)

4. GUI Programs are Event Driven
Signal that something “interesting” has happened
Example: user presses a button, user moves the mouse
Main program reacts to events
while(true){
Wait for an event
React to it }

5. Sequential vs Event-Driven
Programmer is in complete control
Program causes a sequence of actions
Event driven
User is in complete control
User causes events, events cause program actions
“flow of control” - control structures vs. events

6. Major Libraries Used
Abstract Window Toolkit (java.awt.*) - for generating graphics
Rectangle, Polygon, etc.
AWT events (java.awt.event.*)
ActionEvent, MouseEvent, etc.
SWING (javax.swing.*) - for generating units to interact with (some units generate events)
Frames (windows)
Buttons
Labels & Text information

7. Some Swing Classes JFrame JLabel JTextField JTextArea JButton
Represents window with title & border
JLabel
Displays text or an image (cannot be changed)
JTextField
Area for the user to enter one line of text
JTextArea
Area for the user to enter multiline text
JButton
A push button (to connect to an action)

8. Structure of a GUI Program
Main method
Creates an instance of a GUI class
GUI class (implements ActionListener)
Constructor configures components
Action Performer processes events
Event dispatcher
The while loop that waits for events and calls the action performer
You don’t have to write this.
Other listeners exist, e.g. window listener, mouse listener

9. WindChill Calculator Puts up a window with
1 JTextArea (not to be edited)
3 Jlabels (F temp., wind, windchill)
3 JTextFields (one for each label)
1 Jbutton (“Run)
When “Run” is clicked, windchill temp. is computed & displayed in its field, using text from F temp & wind fields
Run this.

10. WindChill Calculator Pseudocode
public class Windchill implements ActionListener {
static final variables for setup info
instance variables for components
window, labels, textfields, etc.
public Windchill() //constructor
public void actionPerformed(ActionEvent e) //event processor }

11. Constructor Configure GUI window.setVisible(true); //after all that!
Set window size & default close operation
Specify properties of objects, e.g. legendArea is not editable
Register event listener (associate it with the button that sends the event)
Arrange components in the GUI
window.setVisible(true); //after all that!

12. Registering Event Listeners
Every object that can send an event needs to be associated with a Listener object that processes that event (using its ActionPerformed method)
Usually, the code to set this up is in the Listener’s constructor
Example (“this” is the ActionListener class):
runButton.addActionListener(this);

13. Arranging Interface Objects
Every JFrame has a LayoutManager that determines locations of new components
FlowLayout - each added object goes to the right of previous object (or below if there isn’t room to the right)
GridLayout - objects are arrayed in a specified number of columns and/or rows
JFrame’s add method places each interface component according to the layout
E.g. window.add(legendArea);

14. ActionPerformed Takes one parameter, an ActionEvent In this case:
One ActionPerformed method can handle several different actions (using a case statement)
In this case:
Event is when runButton is pressed
Action is to compute the windchill and display it in the appropriate text area