java 两个日期之间的天数

private static int numDays(String start,String end){
        Calendar startCal=Calendar.getInstance();
        String arr[]=start.split("-");
        startCal.set(Integer.parseInt(arr[0]), Integer.parseInt(arr[1]), Integer.parseInt(arr[2]));
        long startTime=startCal.getTimeInMillis();
        arr=end.split("-");
        Calendar endCal=Calendar.getInstance();
        endCal.set(Integer.parseInt(arr[0]), Integer.parseInt(arr[1]), Integer.parseInt(arr[2]));
        long endTime=endCal.getTimeInMillis();
        int num=Integer.parseInt(String.valueOf((endTime-startTime)/(1000*60*60*24)));
        return num;
    }