Re-Initializing Date object in a Thread

Question

Hi ppl,
I am actually using a Thread, in which i check the current system time, to perform an operation.
I use a GreagorianCalendar Object to get the Current Time.
Calendar d = new GregorianCalendar();The time value stored in the object remains the same throughout the process. Therefore, i reinitialize the object every Millisecond to update the object with the current time.
d = new GregorianCalendar();Is there any other optimal way to perform this ?
If this is the only way possible, does it, in any way, affect the Memory, since Object is reinitialized every millisecond. If so, what could be the best possible solution ?
Code :
To perform a particular operation at 09:00:00:000
import java.util.Calendar;
import java.util.GregorianCalendar;
public class SampleThread implements Runnable{
     public void run() {
          try
               Calendar d = new GregorianCalendar();
               while(d.get(Calendar.HOUR)!= 9 ||
                         d.get(Calendar.MINUTE)!=0 ||
                         d.get(Calendar.SECOND) != 0 ||
                         d.get(Calendar.MILLISECOND) != 0 )
                    Thread.currentThread().sleep(1);
                    d = new GregorianCalendar();
               System.out.println("Operation Executed at : "+d.getTime());
               Thread.currentThread().sleep(1000);
               d = new GregorianCalendar();
               Thread.currentThread().run();
          catch (InterruptedException e)
               e.printStackTrace();
     public static void main(String a[])
          SampleThread st = new SampleThread();
          Thread t = new Thread(st);
          t.start();
}can the above code be optimized in any way ?

Answer 1

Hi,
Your problem is not the TimerTask, but the way you compute a specific time. Run the following program and you will see what is wrong:
import java.text.DateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
public class Tomorrow {
    public static void main(String[] args) {
     DateFormat dateFormat = DateFormat.getDateTimeInstance(DateFormat.LONG,
          DateFormat.LONG);
     System.out.println("Your start time is today:       "
          + dateFormat.format(getTomorrowMorning4am()));
     System.out.println("Correct start time is tomorrow: "
          + dateFormat.format(tomorrow9am()));
    private static Date getTomorrowMorning4am() {
     Calendar tomorrow = new GregorianCalendar();
     Calendar result = new GregorianCalendar(tomorrow.get(Calendar.YEAR),
          tomorrow.get(Calendar.MONTH), tomorrow.get(Calendar.DATE), 9, 0);
     return result.getTime();
    private static Date tomorrow9am() {
     Calendar calendar = Calendar.getInstance();
     calendar.add(Calendar.DAY_OF_YEAR, 1);
     calendar.set(Calendar.HOUR_OF_DAY, 9);
     calendar.set(Calendar.MINUTE, 0);
     calendar.set(Calendar.SECOND, 0);
     calendar.set(Calendar.MILLISECOND, 0);
     return calendar.getTime();
}The start time you supply has already been expired when you invoke scheduleAtFixedRate.
There is a second problem: the interval. What will happen when daylight saving time comes into effect?
In your case, scheduling at a specific time of the day, you may consider canceling the timertask after completion and schedule a new timertask.
Piet