Java Data Type - 如何计划任务的特定时间

import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Timer;
import java.util.TimerTask;

public final class Main extends TimerTask {
  public static void main(String... arguments) {
    TimerTask fetchMail = new Main();
    // perform the task once a day at 4 a.m., starting tomorrow morning
    Timer timer = new Timer();
    timer.scheduleAtFixedRate(fetchMail, getTomorrowMorning4am(), fONCE_PER_DAY);
  }
  @Override
  public void run() {
    System.out.println("doing");
  }
  private final static long fONCE_PER_DAY = 1000 * 60 * 60 * 24;

  private final static int fONE_DAY = 1;
  private final static int fFOUR_AM = 4;
  private final static int fZERO_MINUTES = 0;

  private static Date getTomorrowMorning4am() {
    Calendar tomorrow = new GregorianCalendar();
    tomorrow.add(Calendar.DATE, fONE_DAY);
    Calendar result = new GregorianCalendar(tomorrow.get(Calendar.YEAR),
        tomorrow.get(Calendar.MONTH), tomorrow.get(Calendar.DATE), fFOUR_AM,
        fZERO_MINUTES);
    return result.getTime();
  }
}