getting a Date that is 30 days ago from today

[kay lin]

Hi All, I want to display a Date that is 30 days ago from today, and I used Date object here is my code,

 
 Date to = new Date();
      //this line is supposedly to get the date that is 30 days ago
       Date from = new Date(to.getTime()-1000*60*60*24*30);
 
       //I know getYear() is deprecated, I just want to use it as a quick test
       System.out.println("from yyyy is " + from.getYear());
 
       System.out.println("from month is " + from.getMonth());
 

However, the display result is incorrect. i.e. The month value is incorrect, today is Jun 4, so 30 days ago, the month should be May (which is 4 numerically). can somebody tell me what i did wrong, or rather, let me know if I should use something different to get the date that is 30 days ago

thanks

[Paul Sturrock]

I think you should have a look at the Calendar object and its roll(int field, int value) method, which you should find a little easier to use.

[kay lin]

Originally posted by Paul Sturrock:
I think you should have a look at the Calendar object and its roll(int field, int value) method, which you should find a little easier to use.

But the roll methods only takes care of the field you use, not the larger fields though. For example, if today is June 4, and I want it to be 30 days ago, then only the Day dispaly will be correct not the month, any other suggestions?

[Carl Trusiak]

The simple answer is found if you do

System.out.println(1000 * 60 * 60 * 24 * 30);

Result -1702967296

You are overflowing an int, that why Date uses a long.

Try
Date from = new Date( to.getTime() - 1000L*60L*60L*24L*30L);

Force these to a long!

Of course the Calendar is a great suggestion

      Calendar cal = new GregorianCalendar();
      Calendar cal2 = new GregorianCalendar();
      cal.roll(Calendar.DAY_OF_YEAR, -30);
      //if within the first 30 days, need to roll the year as well
      if(cal.after(cal2)){
          cal.roll(Calendar.YEAR, -1);
      }
      System.out.println("Year " + cal.get(Calendar.YEAR));
      System.out.println("Month " + cal.get(Calendar.MONTH));
      System.out.println("Day " + cal.get(Calendar.DAY_OF_MONTH));

[Jim Yingst]

You can also use Calendar's add() method rather than roll(), to make things simpler. And note that Date's getXXX() methods are deprecated. Better to use a SimpleDateFormat, or a Calendar, to extract this info from a Date. (Or use the Date's toString() method, which may be exactly what you want.)