Date arithmetic

[Simon Good]

Hi
How do I go about calculating the number of days between two dates? Is there a simple way to do it?
Thanks

[Michael Dunn]

Depends on what answer you want
how many days between monday and friday - 5?
how many days between 15th and 19th - 4?
actual days in-between 15th and 19th = 3
You can convert the dates to milliseconds, then subtract dt1 from dt2, then
convert the result back to days.
Here's a way where you can easily change the code, depending on the output
you want.

import javax.swing.JOptionPane;
import java.util.*;
class DaysDiff
{
  public DaysDiff()
  {
    try
    {
      Calendar cal1 = Calendar.getInstance();
      Calendar cal2 = Calendar.getInstance();
      String bits[];
      bits = JOptionPane.showInputDialog("1st date (yyyy mm dd): ").split(" ");
      cal1.set(Integer.parseInt(bits[0]),Integer.parseInt(bits[1])-1,Integer.parseInt(bits[2]));
      bits = JOptionPane.showInputDialog("2nd date (yyyy mm dd): ").split(" ");
      cal2.set(Integer.parseInt(bits[0]),Integer.parseInt(bits[1])-1,Integer.parseInt(bits[2]));
      int diff = 0;
      
      //test input cal1 == 2004 3 15
      //           cal2 == 2004 3 19
      
      //cal1.add(Calendar.DATE,1); //)
      //while(cal1.before(cal2))   //) days diff == 3
      
      //while(cal1.before(cal2)) //days diff == 4
      
      while(!cal1.after(cal2)) //days diff == 5
      {
        cal1.add(Calendar.DATE,1);
        diff++;
      }
      JOptionPane.showMessageDialog(null,"Days difference = "+diff);
    }
    catch(Exception e)
    {
      JOptionPane.showMessageDialog(null,"Error - terminating");
    }
    System.exit(0);
  }
  public static void main(String args[]){new DaysDiff();}
}