Converting a Date to a Double. How?

Question

I need to be able to a Date to a double in the "days since 12/30/1899 . fractional part is time format".
This is the format use in OLE 2.0 Automation as well as languages such as Delphi.
Any ideas?

Answer 1

I assume this format (double) is the same format used for a MS date and if this is the case MS uses a base date (zero) of "Dec. 30, 1899 12:00:00 AM.". To take the 12:00:00 AM time into consideration when converting your date you should use a Java base date of "Dec. 29, 1899 23:00:00.000 GMT" or -2209147200000L as a long. Here is the code I use to convert between Java dates (long) and MS dates (double):
import java.util.Date;
public class MSDate extends Date {
   private final static int MILLISECONDS_IN_A_DAY = 86400000;
   private final static long MS_BASE_DATE = -2209147200000L; // December 29, 1899, 23:00:00.000 GMT.
   /** Allocates a MSDate object and initializes it so that it
       represents the time at which it was allocated, measured to the
       nearest millisecond. */
   public MSDate() {
      super();
   /** Allocates a MSDate object and initializes it to represent the
       specified number of milliseconds since the standard base time
       known as "the epoch", namely January 1, 1970, 00:00:00 GMT. */
   public MSDate(long date) {
      super(date);
   /** Allocates a MSDate object using the given MS date. */
   public MSDate(double MSDate) {
      this.setMSDate(MSDate);
   /** Sets this MSDate object to represent the MS date (double) provided. */
   public void setMSDate(double MSDate) {
      double dMilliseconds;
      // Convert MS Date (double) to the number of milliseconds since January 1, 1970, 00:00:00.000 GMT.
      dMilliseconds = MSDate * MILLISECONDS_IN_A_DAY;
      // Add MS's base date.
      dMilliseconds += MS_BASE_DATE;
      super.setTime(Math.round(dMilliseconds));
   /** Returns a MS date (double) that represented by this MSDate object. */
   public double getMSDate() {
      double dMSDate = 0;
      double dMilliseconds;
      // Get the number of milliseconds since January 1, 1970, 00:00:00.000 GMT.
      dMilliseconds = this.getTime();
      // Subtract MS's base date.
      dMilliseconds -= MS_BASE_DATE;
      // Convert milliseconds back to a MS date (double).
      dMSDate = dMilliseconds / MILLISECONDS_IN_A_DAY;
      // Return the MS date.
      return dMSDate;
}The only thing that I have noticed is that MS (VB) doesn't display the milliseconds, so a MS date gets rounded up by one second if your Java date has more then 500 milliseconds.