class UserComparator implements Comparator<User> {    public int compare(User u1, User u2) {        if (u1.number.charAt(0) == u2.number.charAt(0)) {            // 如果两人的号都是A开头或者都是V开头,比较号的大小:            //return u1.number.compareTo(u2.number);            //比较数字            int value1=Integer.parseInt(u1.number.substring(1,u1.number.length()));            int value2=Integer.parseInt(u2.number.substring(1));            if(value1>value2){                return 1;            }else if(value1==value2){                return 0;            }            return -1;        }        if (u1.number.charAt(0) == 'V') {            // u1的号码是V开头,优先级高:            return -1;        } else {            return 1;        }    }}