Date; Previous date, Calendar; Gregorian

[Anonymous]

Good day everyone.
I am somewhat stuck on something that seems so simple.
Q: I am trying to write a small app. which will accept the current day of a year and output the correct previous day and DATE. This should take into regards Leap year difference and anything else. I'd like to be able to do this possibly using 1 or a few of the methods that the Java API offers. Any assistance on this would be greatly appreciated.
Thanks

[Carl Trusiak]

This isn't as easy as it may look at first, Ther isn't an easy way to creat a Calendar or GregorianCalendar object from a string and any method to change a date is depricated. After some study a possible solution is :

import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Calendar;
import java.text.SimpleDateFormat;
import java.text.ParseException;
import java.io.*;
public class Yesterday {
  public static void main(String carl[])
  {
     SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
     GregorianCalendar gc = new GregorianCalendar();
     System.out.println("Enter a Date in mm/dd/yyyy format");
     String dateIn = readLine();
     Date d = null;
     try
     { 
        d = sdf.parse(dateIn);
     }
     catch(ParseException pe)
     {
        System.out.println("Incorrect date format");
        System.exit(1);
     }
     gc.setTime(d);
     System.out.println("Todays Date = " + sdf.format(d));
     int dayBefore = gc.get(Calendar.DAY_OF_YEAR);
     gc.roll(Calendar.DAY_OF_YEAR, -1);
     int dayAfter = gc.get(Calendar.DAY_OF_YEAR);
     if(dayAfter > dayBefore)
        gc.roll(Calendar.YEAR, -1);
     gc.get(Calendar.DATE);//this forces the syncing of all the GergorianCalendar fields
     Date d2 = gc.getTime();
     System.out.println("Yesterdays Date = " + sdf.format(d2));
  }
  public static String readLine()
  {
     char input[] = new char[1025];
     try{
         BufferedReader in = new BufferedReader(
                             new InputStreamReader(System.in));
         in.read(input, 0 ,1024);
     }catch(IOException ioe){return "";} 
     return new String(input);
  }
  
}

The output is now
Enter a Date in mm/dd/yyyy format
03/01/2000
Todays Date = 03/01/2000
Yesterdays Date = 02/29/2000
-and-
Enter a Date in mm/dd/yyyy format
03/01/1900
Todays Date = 03/01/1900
Yesterdays Date = 02/28/1900
-and-
Enter a Date in mm/dd/yyyy foramt
01/01/2000
Todays Date = 01/01/2000
Yesterdays Date = 12/31/1999

This is better I hope


[This message has been edited by Carl Trusiak (edited September 22, 2000).]

[Anonymous]

Carl,
Thank you very much. I appreciate this. I had 1st thought it
was quite simple, but as I looked at it more closely, I saw
small problems. I suppose I was hoping for a buildt method
within the java.util.Date or Calendar classes for automatically
being able to convert dates. And even when I did mess around
with the logic, I ended up solving most of the problems but
leaving behind a few critical points. Thank you very much.
Feel free to ask any Qs as well.

Saurav

[Darwin Perez]

ur java date is very good- how about date in words?