1	CS110 Lecture 25 Tuesday, May 4, 2004 Announcements final exam Thursday, May 20, 8:00 AM McCormack, Floor 01, Room 0608 (easier than last Tuesday’s!) wise0 due tonight Agenda Questions (WISE and otherwise) Persistence GUI programming Interfaces
2	Persistence Bank and Juno should remember state between invocations read state from a file at startup write state back to file at exit Can imagine a text representation of the state Better: Java knows how to save whole Objects
3	Bank (version 9) Bank instance can be saved to a file java Bank –f bankFileName live demo … if –f bankFileName && file exists read Bank from that file else create new Bank() visit bank if –f bankFileName write Bank to that file
4	Bank (version 9) public class Bank implements Serializable java Bank –f bankFileName if (bankFileName == null) { theBank = new Bank( bankName ); } else { theBank = readBank ( bankName, bankFileName ); }
5	Read Bank instance from a file private static Bank readBank( String bankName, String bankFileName) { File file = new File( bankFileName ); if (!file.exists()) { return new Bank( bankName ); } ObjectInputStream inStream = null; try { inStream = new ObjectInputStream( new FileInputStream( file ) ); Bank bank = (Bank)inStream.readObject(); System.out.println( "Bank state read from file " + bankFileName); return bank; }
6	Why read/write only Bank? BankAccount and Month are also Serializable Bank box-and-arrow picture shows that all objects of all types are pointed to (indirectly) by arrows starting in the Bank private transient Terminal atm; Terminal not saved when Bank is saved
7	Serializable new Java keyword implements, as in public class Bank implements Serializable {. . .} Serializable is an interface, not a class Find out about interfaces in cs210 (and a little bit soon) Java 1.5 does a cleaner job with persistence
8	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
9	10/joi
10	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
11	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);
12	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
13	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 }
14	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 }
15	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 }
16	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); }
17	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>
18	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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20	All together now public class JOIApplet extends Applet implements ActionListener { ... public void actionPerformed ( ActionEvent e ) { currentMessage = currentMessage.equals(MESSAGE1) ? MESSAGE2 : MESSAGE1; this.repaint(); }
21	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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