Is it possible to generate a random date with gregorian calendar?

[michael montalbano]

The code I have so far is :

import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Random;

public class gregorian {
	
  public static void main(String[] args) {
	int month, year, day;
	  Random call = new Random();
	  month = call.nextInt(11);
	  year = call.nextInt(2010) + 2007;
	  day  = call.nextInt(30);

	   GregorianCalendar calendar = new GregorianCalendar(year, month, day);
    Date now = calendar.getTime();
    System.out.println(now);
  }
}

It is not working. I don't know how to get it so that it will be random.

[michael montalbano]

nevermind, just figured it out.

[Jesper de Jong]

michael montalbano wrote:year = call.nextInt(2010) + 2007;

This will generate a random year between 2007 and 4016. Is that really what you meant?

[michael montalbano]

Yeah i changed it so that it's between 2007 and 2011 so it's good now. I need to have the date be formatted as, for example 'Thursday, 11/13/05 10:55pm' and it is currently formatted as Thur Jul 13 19:06:00 PDT 2005.

[Bear Bibeault]

Dates don't have formats. Strings have formats. Use SimpleDateFormatter to format a data any way you want.

[Campbell Ritchie]

michael montalbano wrote: . . .
month = call.nextInt(11);
. . .

Don’t use number literals like that. Use

    month = call.nextInt(Calendar.DECEMBER) + Calendar.JANUARY;

I shall add code tags to your post, and you can see how much better it looks.

[Campbell Ritchie]

And how on earth do you get 11 to appear as July?

Another possibility is to create a String with the format method and the % tags, as seen here or here.

[Carey Brown]

This will leave out December:
month = call.nextInt(11);

This doesn't work. Day starts with 1 not zero. This will generate a maximum day of 29 which will be wrong in almost all cases.
day = call.nextInt(30);

A better way would be to compute a random number of milli-seconds and convert that to a date. The limiting factor here is that the date will be >= Jan 1, 1970.

I suggest you read up on Random.nextInt() and GregorianCalendar.

[Paul Clapham]

Michael's code does produce random dates. It doesn't produce all dates with equal probability (as you say it is unable to produce some dates at all) but then that wasn't a stated requirement.

Your suggestion works much better at producing all dates with equal probability, but when you render those dates in a particular time zone then days when daylight saving time begin are chosen 23/24 as often as other days (since those days only have 23 hours). On the other hand you don't have that problem if you render them in UTC, so probably that would be the thing to do if this level of detail was important.

[Rob Spoor]

Campbell Ritchie wrote:

michael montalbano wrote: . . .
month = call.nextInt(11);
. . .

Don’t use number literals like that. Use

    month = call.nextInt(Calendar.DECEMBER) + Calendar.JANUARY;

I shall add code tags to your post, and you can see how much better it looks.

That should be

month = call.nextInt(Calendar.DECEMBER - Calendar.JANUARY + 1) + Calendar.JANUARY;

Since Calendar.JANUARY == 0 you could also use Calendar.DECEMBER + 1, but you need the + 1 or you'll never generate December itself.

[Campbell Ritchie]

Yes, you are right, Rob. Sorry.