GUI clock
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import java.applet.Applet;
import java.awt.Graphics;
import java.text.DateFormat;
import java.util.Calendar;
import java.util.Date;
public class GUIClock extends Applet implements Sleeper {
private AlarmClock clock;
public void init() {
clock = new AlarmClock();
}
public void start() {
clock.letMeSleepFor(this, ONE_SECOND);
}
public void paint(Graphics g) {
Calendar cal = Calendar.getInstance();
Date date = cal.getTime();
DateFormat dateFormatter = DateFormat.getTimeInstance();
g.drawString(dateFormatter.format(date), 5, 10);
}
public void wakeUp() {
repaint();
clock.letMeSleepFor(this, ONE_SECOND);
}
}
interface Sleeper {
public void wakeUp();
public long ONE_SECOND = 1000; // in milliseconds
}
class AlarmClock {
private static final int MAX_CAPACITY = 10;
private static final int UNUSED = -1;
private static final int NOROOM = -1;
private Sleeper[] sleepers = new Sleeper[MAX_CAPACITY];
private long[] sleepFor = new long[MAX_CAPACITY];
public AlarmClock() {
for (int i = 0; i < MAX_CAPACITY; i++)
sleepFor[i] = UNUSED;
}
public synchronized boolean letMeSleepFor(Sleeper s, long time) {
int index = findNextSlot();
if (index == NOROOM) {
return false;
} else {
sleepers[index] = s;
sleepFor[index] = time;
new AlarmThread(index).start();
return true;
}
}
private synchronized int findNextSlot() {
for (int i = 0; i < MAX_CAPACITY; i++) {
if (sleepFor[i] == UNUSED)
return i;
}
return NOROOM;
}
private synchronized void wakeUpSleeper(int sleeperIndex) {
sleepers[sleeperIndex].wakeUp();
sleepers[sleeperIndex] = null;
sleepFor[sleeperIndex] = UNUSED;
}
private class AlarmThread extends Thread {
int mySleeper;
AlarmThread(int sleeperIndex) {
super();
mySleeper = sleeperIndex;
}
public void run() {
try {
sleep(sleepFor[mySleeper]);
} catch (InterruptedException e) {
}
wakeUpSleeper(mySleeper);
}
}
}
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