1. Lecture 19 Graphics User Interfaces (GUIs)

2. User Interface The way in which the user interacts with the program
Separate “what” the program does from “how” the user interacts with it
Television
Function: Adjust volume, channels, color, etc
Interface:
Manual controls
Universal Remote
Automobile
Function: Turn, accelerate, decelerate, stop
Human driver
Autonomous vehicle
Project 3’s Forest
Function: Add rocks, trees, weeds, grass, foxes, mice, rabbits
Files
Console
Graphical
- DARPA Urban Challenge

3. Powerball Example
Here’s an example using a class called PowerBallMachine. It is based on the Powerball lottery where a person must correctly match 5 balls selected from a collection of 55 balls.
PowerballMachine has a single method called getOdds(int n, int k). getOdds computes the chances of correctly selecting k balls from a collection of size n.
Let’s look at two interfaces for out PowerBallMachine. The first will be a text based interface and the second with be a graphical interface.
import java.util.*;
public class PowerBallMachine {
public int getOdds(int n, int k) {
int lotteryOdds = 1;
for (int i = 1; i <=k; i++) {
lotteryOdds = lotteryOdds * (n-i+1)/i; }
return lotteryOdds;

4. Powerball- Console Interface
import java.util.*;
public class PowerBallMain {
public static void main(String args[]) {
PowerBallMachine machine = new PowerBallMachine();
Scanner input = new Scanner(System.in);
System.out.println("Enter number of balls to pick from: ");
int n = input.nextInt();
System.out.println("How many balls do you want to draw? ");
int k = input.nextInt();
System.out.println("Odds of winning are 1 in " + machine.getOdds(n, k)); }

5. Powerball – Graphical User Interface

6. Building Graphical User Interfaces
Abstract Window Toolkit versus Swing
AWT depend on native code (heavyweight)
Faster than swing
Not portable
Swing is pure java (lightweight)
Portable
Not necessarily good for graphics
Pros and Cons: see

7. Swing Components Frames Scroll Panes Panels Tabbed Panes Split Panes
Everything builds off of the Frame!
Panels
Tabbed Panes
Split Panes
Sun’s Java Tutorial

8. Swing Components Progress Bars Lists Buttons Combo Boxes Labels
Text Boxes
Menus
Spinners
Sliders
Sun’s Java Tutorial

9. Anatomy of a Frame

10. Swing Components Interact with your Program
PowerballMachine
getOdds(int n, int k)
Your program needs to know when the user enters a number in one of the two text fields so it can call getOdds to get the updated odds. Likewise, it needs to know when the user presses the Run button for the same reason. When the user presses the Exit button your program needs to know that as well so that it can shut down.
The notification occurs via objects called Events. Every time a GUI component changes it’s state, it generates an event and sends the event to any object that is interested. An object lets the GUI component know that it is interested the events by registering as an event listener with the GUI component.

11. Event Handling Graphical User Interface Widget Event Listeners or
Object A
Object B
Object C
Event
Event
Event
Widget
Registered Listeners
Object A
Object B
Object C
Event Listeners or
Event Handlers

12. Creating & Sending Events
GUI components that can change state, generate “events” when a change occurs
JButtons – ActionEvent
JTextField – ActionEvent
JLists – ListSelectionEvent
JCheckBox – ItemEvent
plus many, many more...
All have a method which allows objects to register as an event listener
addxxxListener(xxxListener x);
Events are not limited to GUI components, however they will be introduced and discussed in that context

13. Event Listeners/Handlers
Objects become event listeners by implementing the appropriate interface that will allow them to register with a GUI component that generates events
Ex: JButton is a GUI component that generates events every time it is pressed
JButton b = new JButton(“Button #1”);
Generate ActionEvents
addActionListener(ActionListener a);
Any object implementing the ActionListener interface can register with the JButton to be notified when the button changes state (is pressed)
public interface ActionListener {
void actionPerformed(ActionEvent e); }
public class MyObject implements ActionListener {
...
public void actionPerformed(ActionEvent e) {
System.out.println(“Don’t press the button!”);
MyObject mo = new MyObject();
b.addActionListener(mo);
By virtue of being a JButton, b generates ActionEvents
By implementing the ActionListener interface, MyObject becomes an ActionListener
Since mo is an ActionListener, it can register with JButton b

14. Button Example
We’re going to start with a very simple example with a Frame that contains two GUI components
a button
a label.
When the button is pressed, a message is displayed at the console

15. GuiTest extends JFrame
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class GuiTest extends JFrame {
private Container c;
public GuiTest(String t) {
super(t);
setSize(275, 170);
c = getContentPane();
c.setLayout(new FlowLayout());
JButton b = new JButton("I Believe");
b.addActionListener(new MyActionListener());
c.add(b);
JLabel lab = new JLabel("Push the button!");
c.add(lab);
setVisible(true);
addWindowListener(new MyWindowAdapter()); }
public static void main(String[] args) {
GuiTest g = new GuiTest("GuiTest Title");
class MyWindowAdapter extends WindowAdapter {
public void windowClosing(WindowEvent e) {
System.out.println("Window closed...Exiting Program");
System.exit(0);
class MyActionListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
System.out.println("Button Pressed");
GuiTest extends JFrame
Compare this version to the previous. Things to note:
The explicit definition of a JFrame is gone. GuiTest extends JFrame so it is the JFrame.
Most of what was in main is now in the GuiTest constructor.
The title for the frame is passed via the constructor using super.
Notice that we have three separate classes

16. GuiTest: Inner Classes
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class GuiTest1 extends JFrame {
private Container c;
public GuiTest1(String t) {
super(t);
setSize(275, 170);
c = getContentPane();
c.setLayout(new FlowLayout());
JButton b = new JButton("I Believe");
b.addActionListener(new MyActionListener());
c.add(b);
JLabel lab = new JLabel("Push the button!");
c.add(lab);
setVisible(true);
addWindowListener(new MyWindowAdapter()); }
public static void main(String[] args) {
GuiTest1 g = new GuiTest1("GuiTest Title");
class MyWindowAdapter extends WindowAdapter {
public void windowClosing(WindowEvent e) {
System.out.println("Window closed...Exiting Program");
System.exit(0);
class MyActionListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
System.out.println("Button Pressed");
Here’s we’ve brought all three into a single class and had GuiTest extend JFrame. We’ve also moved most of it to the constructor.

17. GuiTest: Count the button clicks
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class GuiTest3 extends JFrame {
private Container c;
private int x = 0;
JLabel lab;
public GuiTest3(String t) {
super(t);
setSize(275, 170);
c = getContentPane();
c.setLayout(new FlowLayout());
JButton b = new JButton("I Believe");
b.addActionListener(new MyActionListener());
c.add(b);
lab = new JLabel("Push the button!");
c.add(lab);
setVisible(true); }
public static void main(String[] args) {
GuiTest3 g = new GuiTest3("GuiTest Title");
g.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
class MyActionListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
x++;
if (x == 1) {
lab.setText("First Time!");
System.out.println("Button pressed for
the first time!"); }
else if (x < 10) {
lab.setText(x + " times.");
System.out.println("Button Pressed " +
x + " times.");
else {
lab.setText("Enough already...stop!");
We did two things here, we got rid of the WindowAdapter and we also added some additional functionality to the ActionListener
If we had not made MyActionListener an inner class then we would not be able to change the label and count the clicks.