JAVA:計算從今天到某天一共有多少天

import java.util.Calendar;
public class Date_Something {
public static void main(String[] args) {
Calendar today = Calendar.getInstance();
Calendar someday = Calendar.getInstance();
someday.set(2012,9,13);
System.out.println(today.getTimeInMillis());
System.out.println(someday.getTime());
System.out.println("離 "+someday.get(someday.YEAR)+"/"+(someday.get(someday.MONTH)+1)+"/"+someday.get(someday.DATE)+"剩"+(someday.getTimeInMillis()-today.getTimeInMillis())/ (1000 * 60 * 60 * 24)+"天");
}
}