Lösningsförslag till exempeldugga

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1 till exempeldugga 1 (6) Kursnamn Objektorienterade applikationer Program DAI 2 Examinator Uno Holmer Modellering Designmönster a) Decorator. b) public class Singleton { private static Singleton instance = null; // Private prevents external object creation private Singleton() { // Return the single object of this class // create (lazily) if necessary public static Singleton getinstance() { if ( instance == null ) instance = new Singleton();... return instance;

2 Trådar 2 (6) a) public class ClockLabel extends JLabel implements ActionListener { private int time = 0; Timer t = new Timer(1000,this); // Swing-timer public ClockLabel() { super(" ",JLabel.CENTER); t.start(); public void actionperformed(actionevent e) { settext(integer.tostring(++time)); b) public class DoBackground extends Thread { private Computable obj; private float arg; private float value; private boolean ready = false; public DoBackground(Computable obj,float arg) { this.obj = obj; this.arg = arg; start(); public void run() { value = obj.compute(arg); ready = true; public boolean isready() { return ready; public float getvalue() throws IllegalStateException { if (! ready ) throw new IllegalStateException(); else return value;

3 Kommunikation Koden I fetstil efterfrågades. 3 (6) public static void main(string[] arg) { String hostaddress = arg[0]; int port = Integer.parseInt(arg[1]); InetAddress iadr = InetAddress.getByName(hostAddress); DatagramSocket socket = new DatagramSocket(); Scanner in = new Scanner(System.in); while ( in.hasnextline() ) { byte[] buf = in.nextline().getbytes(); socket.send( new DatagramPacket(buf,buf.length,iadr,port)); catch (Exception e ) { e.printstacktrace(); Trådar Med java.util.timer: public class ReminderTimer { private final long TIME_FACTOR = 60*1000; private Timer timer; public ReminderTimer(long delay,long interval,string msg) { timer = new Timer(); timer.schedule(new ReminderTask(msg), delay*time_factor, interval*time_factor); private class ReminderTask extends TimerTask { private String msg; public ReminderTask(String msg) { this.msg = msg; public void run() { JOptionPane.showMessageDialog( null, msg, "Reminder", JOptionPane.INFORMATION_MESSAGE ); public void kill() { timer.cancel();

4 Alt. med tråd: public class ReminderThread extends Thread { private final int TIME_FACTOR = 1000; private int delay,interval; private String msg; 4 (6) public ReminderThread(int delay,int interval,string msg) { this.delay = delay*time_factor; this.interval = interval*time_factor; this.msg = msg; start(); public void run() { sleep(delay); catch (InterruptedException e) { while (! interrupted() ) { JOptionPane.showMessageDialog( null, msg, "Reminder", JOptionPane.INFORMATION_MESSAGE ); sleep(interval); catch (InterruptedException e) { return; return; public void kill() { stop(); Kommunikation private void senddatagram(string address,string port,string text) { InetAddress toaddr = InetAddress.getByName(address); final int toport = Integer.parseInt(port); DatagramSocket socket = new DatagramSocket(); byte[] data = text.getbytes(); socket.send(new DatagramPacket(data, data.length, toaddr, toport)); catch ( UnknownHostException e ) { catch ( NumberFormatException e ) { catch ( SocketException e ) { catch ( IOException e ) {

5 Strömmmar och filer 5 (6) private void savetofile(string filename,string text) { PrintWriter out = new PrintWriter(new FileWriter(fileName)); Scanner sc = new Scanner(text); int lineno = 1; while ( sc.hasnextline() ) out.println(lineno++ + ". " + sc.nextline()); out.close(); catch (IOException e) { System.out.println("Cannot create " + filename); System.exit(0); GUI public class Gui extends JFrame implements ActionListener { private JTextArea textarea; private JMenuItem eraseitem, saveitem, senditem; Gui() { makeframe(); private void makeframe() { settitle("message sender"); setlayout(new BorderLayout(2,2)); add(new JLabel("Type a message"),borderlayout.north); textarea = new JTextArea(null,10,50); add(textarea,borderlayout.center); makemenubar(); setdefaultcloseoperation(exit_on_close); pack(); setvisible(true); private void makemenubar() { JMenuBar menubar = new JMenuBar(); setjmenubar(menubar); JMenu actionmenu = new JMenu("Actions"); menubar.add(actionmenu); eraseitem = new JMenuItem("Erase"); actionmenu.add(eraseitem); eraseitem.addactionlistener(this); saveitem = new JMenuItem("Save"); actionmenu.add(saveitem); saveitem.addactionlistener(this); senditem = new JMenuItem("Send"); actionmenu.add(senditem); senditem.addactionlistener(this);

6 6 (6) public void actionperformed(actionevent e) { if ( e.getsource() == eraseitem ) { textarea.settext(null); else if ( e.getsource() == saveitem ) { savetofile(getstring("output file name"), textarea.gettext()); else if ( e.getsource() == senditem ) { String[] addrport = getstring("ip address and port number").split(" "); senddatagram(addrport[0],addrport[1],textarea.gettext()); private String getstring(string msg) { String response; do { response = JOptionPane.showInputDialog(null,msg,null, JOptionPane.QUESTION_MESSAGE); while ( response == null ); return response;