Add 30 days to Date in java

Question

why when i add 30 days to today's day i got today's day - 30, and when i add 20 it adds??

here is a sample

import java.text.DateFormat; import java.util.Date;  public class DatePlus {      public static void main(String[] args)     {         Date now = new Date();         Date now1 = new Date();         Date now2 = new Date();         DateFormat currentDate = DateFormat.getDateInstance();          Date addedDate1 = addDays(now2, 20);         Date addedDate2 = addDays(now1, 30);         System.out.println(currentDate.format(now));         System.out.println(currentDate.format(addedDate1));         System.out.println(currentDate.format(addedDate2));     }      public static Date addDays(Date d, int days)     {         d.setTime(d.getTime() + days * 1000 * 60 * 60 * 24);         return d;     } } 

"this is the console"

Jul 30, 2012 Aug 19, 2012 Jul 10, 2012 

Answer 1

Use a Calendar. http://docs.oracle.com/javase/6/docs/api/java/util/GregorianCalendar.html

Pseudo code:

Calendar c= Calendar.getInstance(); c.add(Calendar.DATE, 30); Date d=c.getTime(); 

Answer 2

This is because 30 * 1000 * 60 * 60 * 24 overflows Integer.MAX_VALUE, while 20 * 1000 * 60 * 60 * 24 does not.