Timers

Java runtime system permet à la thread d'utiliser un moniteur déjà obtenu (les moniteurs sont re-entrant). Comme ca on peut éviter autoblocage

public class Reentrant {
 public static void main(String a[]){
 Reentrant r = new Reentrant();
 r.a();
 }
 public synchronized void a() {
	b();
	System.out.println("here I am, in a()");
 }
 public synchronized void b() {
	System.out.println("here I am, in b()");
 }
}

here I am, in b()
here I am, in a()

Timers

Classe

java.util.Timer

Constructor Summary
`Timer()` Creates a new timer.
`Timer(boolean isDaemon)` Creates a new timer whose associated thread may be specified to run as a daemon.
`Timer(String name)` Creates a new timer whose associated thread has the specified name.
`Timer(String name, boolean isDaemon)` Creates a new timer whose associated thread has the specified name, and may be specified to run as a daemon.

Method Summary
`void`	`cancel()` Terminates this timer, discarding any currently scheduled tasks.
`int`	`purge()` Removes all cancelled tasks from this timer's task queue.
`void`	`schedule(TimerTask task, Date time)` Schedules the specified task for execution at the specified time.
`void`	`schedule(TimerTask task, Date firstTime, long period)` Schedules the specified task for repeated fixed-delay execution, beginning at the specified time.
`void`	`schedule(TimerTask task, long delay)` Schedules the specified task for execution after the specified delay.
`void`	`schedule(TimerTask task, long delay, long period)` Schedules the specified task for repeated fixed-delay execution, beginning after the specified delay.
`void`	`scheduleAtFixedRate(TimerTask task, Date firstTime, long period)` Schedules the specified task for repeated fixed-rate execution, beginning at the specified time.
`void`	`scheduleAtFixedRate(TimerTask task, long delay, long period)` Schedules the specified task for repeated fixed-rate execution, beginning after the specified delay.

java.util.TimerTask

Constructor Summary
`protected`	`TimerTask()` Creates a new timer task.

Method Summary
`boolean`	`cancel()` Cancels this timer task.
`abstract void`	`run()` The action to be performed by this timer task.
`long`	`scheduledExecutionTime()` Returns the scheduled execution time of the most recent actual execution of this task.

3.8.1. Exemple - une seule fois

import java.util.Timer;
import java.util.TimerTask;

public class TimerReminder {
    Timer timer;
    public TimerReminder(int seconds) {
        timer = new Timer();
        timer.schedule(new RemindTask(), seconds*1000);
    }
    class RemindTask extends TimerTask {
        public void run() {
            System.out.println("Time's up!");
            timer.cancel(); //Terminate the timer thread
        }
    }
    public static void main(String args[]) {
        System.out.format("About to schedule task.%n");
        new TimerReminder(4);
        System.out.println("Task scheduled.");
    }
}

About to schedule task.
Task scheduled.
Time's up!

3.8.2 Exemple - boucle 3 fois

import java.util.Timer;
import java.util.TimerTask;

/**
* Schedule a task that executes once every second.
*/

public class Beep {
    Timer timer;

    public Beep() {
        timer = new Timer();
        timer.schedule(new RemindTask(),
                0,        //initial delay
                1*1000); //subsequent rate
    }
    class RemindTask extends TimerTask {
        int numWarningBeeps = 3;

        public void run() {
            if (numWarningBeeps > 0) {
                System.out.println("Beep!");
                numWarningBeeps--;
            } else {
                System.out.println("Time's up!");
                timer.cancel();
            }
        }
    }
    public static void main(String args[]) {
        System.out.println("About to schedule task.");
        new Beep();
        System.out.println("Task scheduled.");
    }
}

About to schedule task.
Task scheduled.
Beep!
Beep!
Beep!
Time's up!

Exercises

3.8.3 Un jeu: Si le clique est sur le carré bleu le compteur augmente, si en dehors - le compteur diminue

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Test extends JPanel{
    boolean bleu = true;
    public int x=30,y=30, rd=30;
    Label l = new Label("0");
    int cnt=0;
    Color c;
    public void init(){
        c=Color.blue;
        setForeground(c);
        addMouseListener(new MouseHandler());
        add(l);
    }
    public void paintComponent(Graphics g){
        super.paintComponent(g) ;
        g.fillRect(x, y, rd, rd);
    }
    boolean in (int mx,int my){
        if((mx>x) && (mx<x+rd ))
            if((my>y)&&(my<y+rd)) return true;
        return false;
    }
    class MouseHandler extends MouseAdapter {
        public void mousePressed(MouseEvent e){
             if(in(e.getX(),e.getY())) cnt++;
             else cnt--;
             l.setText(cnt+"");
        }
    }
}
//========================
import javax.swing.JFrame;
public class TestApp {
    public static void main(String arg[]) {
            JFrame frame = new JFrame("Test");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            Test ex = new Test();
            frame.add(ex);
            ex.init();
            frame.setSize(250, 250);
            frame.setVisible(true);
        }
}

3.8.4 Ajouter um timer qui deplace le carré a une position aléatoire une fois par seconde

import java.util.Timer;
import java.util.TimerTask;

import javax.swing.JFrame;
public class Game {
   static Timer move;
   static Test ex;
   static int width=250, height=250;
   public static void main (String arg[]) {
        move =new Timer();
        JFrame frame = new JFrame("Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        ex = new Test();
        frame.add(ex);
        ex.init();
        frame.setSize(width, height);
        frame.setVisible(true);

        move.schedule(new MvTask(),
                1000,        //initial delay
                1*1000); //subsequent rate
   }
   static class MvTask extends TimerTask{
        public void run() {
            ex.x= (int)(Math.random()*(ex.getWidth()-ex.rd));
            ex.y= (int)(Math.random()*(ex.getHeight()-ex.rd));
            ex.repaint();
        }
   }
}

3.8.5 Créer une nouvelle classe - Game2 avec 2 timers:
1) pour deplacer le carré a une position aléatoire une fois par seconde;
2) pour qu'après un click sur le carré, il change sa couleur en rouge pour 0.2 secondes.