java中如何计算出两个日期之间相差多少天

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class Test {
public static void main(String[] args) throws ParseException {
String date1="1987-01-01";
String date2="2010-01-01";
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-mm-dd");
Date d1=sdf.parse(date1);
Date d2=sdf.parse(date2);
long daysBetween=(d2.getTime()-d1.getTime()+1000000)/(3600*24*1000);
System.out.println("1987-01-01 与 2010-01-01 相隔 "+daysBetween+" 天");
}
}