java如何计算两个日期之间相差的天数

看完了jdk的help，发现sun没有提供这样的一个函数，朋友给了几个实现方法//取得剩余天数
SimpleDateFormat df=new SimpleDateFormat("yyyymmdd");
Date d0=new java.util.Date();
Date d1=df.parse(end_date);
long time0=d0.getTime();
long time1=d1.getTime();
System.out.println((time1-time0)/(1000*60*60*24)); 这样算两个时间相差的天数比较好 /**
* 计算两个日期之间相差的天数** @param date1
* @param date2* @return*/public static int diffdates(Date date1, Date date2) {
int result = 0;
ElapsedTime et = new ElapsedTime(); GregorianCalendar gc1 = new GregorianCalendar();
GregorianCalendar gc2 = new GregorianCalendar(); gc1.setTime(date1);
gc2.setTime(date2);
result = et.getDays(gc1, gc2); return result;}然后ElapseTime中的方法是：
public int getDays(GregorianCalendar g1, GregorianCalendar g2) {
int elapsed = 0;
GregorianCalendar gc1, gc2; if (g2.after(g1)) {
gc2 = (GregorianCalendar) g2.clone();
gc1 = (GregorianCalendar) g1.clone();} else {gc2 = (GregorianCalendar) g1.clone();
gc1 = (GregorianCalendar) g2.clone();
} gc1.clear(Calendar.MILLISECOND);
gc1.clear(Calendar.SECOND);
gc1.clear(Calendar.MINUTE);
gc1.clear(Calendar.HOUR_OF_DAY); gc2.clear(Calendar.MILLISECOND);
gc2.clear(Calendar.SECOND);
gc2.clear(Calendar.MINUTE);
gc2.clear(Calendar.HOUR_OF_DAY); while (gc1.before(gc2)) {
gc1.add(Calendar.DATE, 1);elapsed++;}return elapsed;}其实使用joda最简单public boolean isRentalOverdue(DateTime datetimeRented) {