Java Timer

alaios · 05-23-2004, 01:00 PM

Hi do u know how i can make a textbox to show the time? I also want to update the values at each sec

eric.r.turner · 05-23-2004, 05:22 PM

Use the java.swing.Timer class. The Timer needs a class that implements the ActionListener interface, so basically you write a class that implements that interface. In the actionPerformed method you just increment the seconds of a Calendar object, and use the DateFormat class to format the date for the text field. An example is probably easier than trying to explain it. Here's a JPanel that does what you need:

Code:

// TimeTestPanel.java

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.DateFormat;
import java.util.Calendar;
import java.util.GregorianCalendar;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.Timer;

public class TimeTestPanel extends JPanel {

   private static final int delay = 1000; // milliseconds
   private static final int textFieldWidth = 20;

   private JTextField        textField = null;
   private Timer             timer = null;

   public TimeTestPanel() {

      textField = new JTextField( textFieldWidth );
      timer = new Timer( delay , new TimerListener() );

      add( textField );
      timer.start();
   }


   class TimerListener implements ActionListener {

      private Calendar calendar = null;
      private DateFormat time = null;

      public TimerListener() {
         calendar = new GregorianCalendar();
         time = DateFormat.getDateTimeInstance();
      }

      public void actionPerformed( ActionEvent event ) {
         calendar.add( Calendar.SECOND , 1 );
         textField.setText( time.format( calendar.getTime() ) );
      }

   }

}

You need to add the panel to a JFrame, so here's the JFrame:

Code:

// TimeTestFrame.java

import java.awt.Dimension;
import java.awt.Point;
import java.awt.Toolkit;
import javax.swing.JFrame;

public class TimeTestFrame extends JFrame {

   public TimeTestFrame() {

      Toolkit toolKit = Toolkit.getDefaultToolkit();
      Dimension screenSize = toolKit.getScreenSize();

      Point frameLocation = new Point( screenSize.width/4 ,
                                       screenSize.height/4 );

      setSize( screenSize.width/2 , screenSize.height/2 );
      setLocation( frameLocation );

      setDefaultCloseOperation( EXIT_ON_CLOSE );
   }

}

This is the main application class that creates the frame and panel, and adds the panel to the frame:

Code:

// TimeTest.java

public class TimeTest {

   public static void main( String[] args ) {

      TimeTestFrame frame = new TimeTestFrame();
      TimeTestPanel panel = new TimeTestPanel();
      frame.getContentPane().add( panel );
      frame.show();

   }

}

german · 05-23-2004, 05:42 PM

This does it in a lot less code:

Code:

import javax.swing.*;
import java.text.SimpleDateFormat;
import java.util.Date;
                                                                                    
public class timer extends Thread {
        private static final String format = "HH:mm:ss a";
        private SimpleDateFormat sdf;
        private JTextField field;
                                                                                    
        public timer(JTextField field) {
                this.sdf = new SimpleDateFormat(format);
                this.field = field;
        }
                                                                                    
	public void run() {
		while(true) {
			SwingUtilities.invokeLater(
				new Runnable() {
					public void run() {
						long time = System.currentTimeMillis();
						Date now = new Date(time);
						field.setText(sdf.format(now));
					}
				}
			);
			try { Thread.sleep(1000); } 
			catch(InterruptedException e) {}			
		}
	}
                                                                                    
        public static void main(String[] args) throws Exception {
                JFrame frame = new JFrame("Timer!");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setSize(300,50);
                JTextField field = new JTextField();
                frame.getContentPane().add(field);
                frame.setVisible(true);
                new timer(field).start();
        }
}

german · 05-24-2004, 11:52 AM

Quote:

Originally posted by eric.r.turner

Code:

      public void actionPerformed( ActionEvent event ) {
         calendar.add( Calendar.SECOND , 1 );
         textField.setText( time.format( calendar.getTime() ) );
      }

This code does not guarantee any relevance to the actual system time, and it will probably lose time since java does not have real-time capabilities. For instance, if the swing event queue has enough stuff in it that the actual time the method gets called is 10ms after exactly 1 second (which is considered an acceptable latency by swing standards, since it has to be called out of the thread which handles all other painting operations), it will start losing seconds and after an hour the time it reflects will be noticeably different than the system time. You're better off setting the time from System.getCurrentTimeMillis() because it gets the value from the native platform's real-time clock (I believe).