I have a small problem but I don't know to fix it. I create simple Applet in which should be simple digital clock. I created all methods correctly but repaint methods doesn't repaint my applet. Can you check my code and say where is mistake. Thanks.
public class DigitalClock extends JApplet implements Runnable {
private Thread timeThread;
Date date = new Date();
public void start() {
timeThread = new Thread(this, "Clock");
timeThread.start();
}
@Override
public void stop() {
if (timeThread == null) {
return;
}
timeThread = null;
}
@Override
public void run() {
while (timeThread != null) {
repaint();
try {
timeThread.sleep(1000);
} catch (InterruptedException e) {
}
}
}
@Override
public void paint(Graphics g) {
date.setTime(System.currentTimeMillis());
g.drawString(date.toString(), 50, 95);
}
}
Just use a javax.swing.Timer
. See how to use Swing Timer
Here's an example. But rather than painting on top-level container like JApplet
which you are doing, I'm painting on JPanel
which is more recommended
import java.awt.*;
import java.awt.event.*;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.swing.*;
public class TimerPanel extends JPanel {
private String dateString;
private final SimpleDateFormat format;
private final Font font;
private final Date date;
public TimerPanel() {
format = new SimpleDateFormat("hh:mm:ss a");
font = new Font("impact", Font.PLAIN, 30);
date = new Date();
date.setTime(System.currentTimeMillis());
dateString = format.format(date);
Timer timer = new Timer(1000, new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
date.setTime(System.currentTimeMillis());
dateString = format.format(date);
repaint();
}
});
timer.start();
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
g.setFont(font);
FontMetrics fm = g.getFontMetrics(font);
int width = fm.stringWidth(dateString);
int height = fm.getAscent();
int x = getWidth() / 2 - width / 2;
int y = getHeight() / 2 + height / 2;
g.drawString(dateString, x, y);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(300, 100);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
TimerPanel timer = new TimerPanel();
JOptionPane.showMessageDialog(
null, timer, "Digital Clock", JOptionPane.PLAIN_MESSAGE);
}
});
}
}
More directly answering your question, your code works when I test it, the only thing you're forgetting to do is call super.paint()
. Works as expected after doing so
@Override
public void paint(Graphics g) {
super.paint(g);
You'll want to avoid Thread.sleep
though. You may notice this causes flickering. It's preferred to use javax.swing.Timer
. That's why I answered with my example first.
Look at this another example. As @peeskillet answer, I also used JPanel
to show time, but in my code I am using JLabel
to show time.
public class ClockPane extends JPanel {
private JLabel clock;
public ClockPane() {
setLayout(new BorderLayout());
clock = new JLabel();
clock.setHorizontalAlignment(JLabel.CENTER);
clock.setFont(UIManager.getFont("Label.font").deriveFont(Font.BOLD, 32f));
tickTock();
add(clock);
Timer timer = new Timer(500, new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
tickTock();
}
});
timer.setRepeats(true);
timer.setCoalesce(true);
timer.setInitialDelay(0);
timer.start();
}
public void tickTock() {
clock.setText(DateFormat.getDateTimeInstance().format(new Date()));
}
public static void main(String args[]){
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
ClockPane clock = new ClockPane();
JOptionPane.showMessageDialog(
null, clock, "Digital Clock", JOptionPane.PLAIN_MESSAGE);
}
});
}
}
You should use a private attribute like
private boolean running = true;
You set it in stop-method to false
. And in run-method you evaluate it as stop condition instead of evaluating timeThread != null
. This procedure is safer because otherwise you get into concurrency problems within run-method caused by NullPointerException
.
And you should check the applet state by watching its console output in browser plugin. Do you see exceptions?
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