Calendar類計算兩個日期之間相差天數

String str1 = "2014-4-27 11:04:20";
String str2 = "2015-5-28 15:04:10";
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
Calendar cal1=Calendar.getInstance();
try {
cal1.setTime(sdf.parse(str1));
Calendar cal2=Calendar.getInstance();
cal2.setTime(sdf.parse(str2));
long l=cal2.getTimeInMillis()-cal1.getTimeInMillis();
int days=new Long(l/(1000*60*60*24)).intValue();
System.out.println("2個日期之間相差："+days+"天。");
} catch (ParseException e) {
e.printStackTrace();
}