// Get today's day and month
Calendar cal = Calendar.getInstance();
Date date = new Date();
cal.setTime(date);
int month = cal.get(Calendar.MONTH);
int day = cal.get(Calendar.DAY_OF_MONTH);
System.out.println("Day is " + day + ", month is " + month);
// Find the date 20 days hence
final long MILLIS_PER_DAY = 24 * 60 * 60 * 1000L;
long offset = date.getTime();
offset += 20 * MILLIS_PER_DAY;
date.setTime(offset);
cal.setTime(date);
// Now get the adjusted date back
month = cal.get(Calendar.MONTH);
day = cal.get(Calendar.DAY_OF_MONTH);
System.out.println("In 20 days time, day will " + day + ", month will be " + month);
System.out.println(cal);
