java Calendar日期相减问题
两个日期相减,必须是Date型变量使用其getTime()后相减,所以如果是从Calendar获得时间,则需:
Calendar date1 = Calendar.getInstance();
Calendar date2 = Calendar.getInstance();

date1.getTime().getTime() - date2.getTime().getTime() ;

结果为long型,毫秒!
实例1:

Calendar cal=Calendar.getInstance();cal.setTime(new java.util.Date());Calendar calendar=Calendar.getInstance();calendar.set(Calendar.HOUR_OF_DAY,21);calendar.set(Calendar.MINUTE,30);calendar.set(Calendar.SECOND,00);StringBuffer stb=new StringBuffer();long between=(calendar.getTime().getTime()-cal.getTime().getTime())/1000;long hour=between/3600;   long minute=between%3600/60;       long second=between%60;stb.append(+hour);stb.append("时");if(minute<10){stb.append("0");}stb.append(minute);stb.append("分");if(second<10){stb.append("0");}stb.append(second);stb.append("秒");