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 Lecture 24 1 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 Lecture 24 2 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 Lecture 24 3 Bank (version 9) public class Bank implements Serializable • java Bank –f bankFileName • if (bankFileName == null) { theBank = new Bank( bankName ); } else { theBank = readBank ( bankName, bankFileName ); } Lecture 24 4 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; Lecture 24 5 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 Lecture 24 6 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 Lecture 24 7 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 Lecture 24 8 10/joi Lecture 24 9 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 Lecture 24 10 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 39 40 button = new Button( "Press Me" ); this.add( button ); font = new Font("Garamond", Font.BOLD, 48); Lecture 24 11 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 Lecture 24 12 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 } Lecture 24 13 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 } Lecture 24 14 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 } Lecture 24 15 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); } Lecture 24 16 Running the program • as an applet from a browser: file joi.html <html> This file is written in html (“hypertext markup language”), <body> not Java. Browsers understand html. <applet code="JOIPanel.class" height=100 width=400> </applet> main method never runs. Execution starts with init. </body> </html> Lecture 24 17 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 Lecture 24 18 Lecture 24 19 All together now public class JOIApplet extends Applet implements ActionListener { ... public void actionPerformed ( ActionEvent e ) { currentMessage = currentMessage.equals(MESSAGE1) ? MESSAGE2 : MESSAGE1; this.repaint(); } Lecture 24 20 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 . Lecture 24 21 java Juno -e -g Lecture 24 22