1	CS110 Lecture 26 Thursday, May 6, 2004 This lecture not delivered from slides Announcements final exam Thursday, May 20, 8:00 AM McCormack, Floor 01, Room 0608 wise1 due next Tuesday Agenda Questions (WISE and otherwise) GUI programming Interfaces
2	GUI Programming Fun some introductory courses start here requires hardware support (PCs) maybe more in CS110 in time GUI syntax: what windows look like - containers and components GUI semantics: how windows behave – event driven programming System does lots of work for you Learn the APIs, use software tools
3	10/joi
4	GUI Syntax (what windows look like) AWT (Abstract Windowing Toolkit) Abstract class Container subclasses: Panel, Window, Frame methods: add, setLayout Abstract class Component subclasses: Button, Checkbox, Textfield, Up to date Java GUI programmers use swing: classes: JButton, JTextfield,… or they use GUI builders
5	Building window look and feel class JOIPanel extends Applet extends Panel init method creates a button and adds it to this Panel, sets font: 38 button = new Button( "Press Me" ); 39 this.add( button ); 40 font = new Font("Garamond", Font.BOLD, 48);
6	Building window behavior Add a listener to the button 43 button.addActionListener( new JOIButtonListener( this ) ); When button is pressed, system sends an actionPerformed message to the listener To see what happens, look at method actionPerformed in class JOIButtonListener
7	JOIButtonListener // constructor remembers the Panel 27 public JOIButtonListener ( JOIPanel panel ) 28 { 29 this.panel = panel; 30 } // send panel a changeMessage message now! 41 public void actionPerformed ( ActionEvent e ) 42 { 43 panel.changeMessage(); 44 }
8	Changing the message In JOIPanel: change the message and ask the system to repaint: 51 public void changeMessage() 52 { 53 currentMessage = 54 currentMessage.equals(MESSAGE1) ? MESSAGE2 : MESSAGE1; 55 this.repaint(); 56 }
9	Changing the message repaint( ) (which is really super.repaint( )) invokes paint( ) A Graphics object is like a programmable pen or paintbrush 67 public void paint(Graphics g) 68 { 69 g.setColor(Color.black); 70 g.setFont(font); 71 g.drawString(currentMessage, 40, 75); 72 }
10	Running the program as an application > java JOIPanel public static void main( String[] args ) { Terminal t = new Terminal(); Frame frame = new Frame(); JOIPanel panel = new JOIPanel(); panel.init(); frame.add(panel); frame.setSize(400,120); frame.show(); t.readLine("return to close window "); System.exit(0); }
11	Running the program as an applet from a browser: file joi.html <html> <body> <applet code="JOIPanel.class" height=100 width=400> </applet> </body> </html>
12	Interfaces An interface is like a very abstract class no fields only abstract methods A class that implements an interface promises to implement its abstract methods public class JOIButtonListener implements ActionListener
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14	All together now public class JOIApplet extends Applet implements ActionListener { ... public void actionPerformed ( ActionEvent e ) { currentMessage = currentMessage.equals(MESSAGE1) ? MESSAGE2 : MESSAGE1; this.repaint(); }
15	Interfaces in Collection framework Inheritance hierarchy (classes) java.lang.Object java.util.AbstractMap java.util.TreeMap TreeMap implements interfaces: Cloneable, Map, Serializable, SortedMap AbstractMap implements Map Map foo = new TreeMap( ) // legal
16	Juno 10 has a GUI Juno CLI prompts for input when it wants it => the program is in control Juno GUI sits waiting for user input from anywhere mouse can go, then takes action => the user is in control (event driven) > java Juno –g .
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