判断周几

题目：请输入星期几的第一个字母来判断一下是星期几，如果第一个字母一样，则继续判断第二个字母。

public class Arithmetic_weekOfDay {
    public static void main(String[] args) {
        //Monday Tuesday Wednesday Thursday Friday Saturday Sunday
        Scanner sc = new Scanner(System.in);
        List<String> ls = new ArrayList<String>();
        ls.add("Monday");
        ls.add("Tuesday");
        ls.add("Wednesday");
        ls.add("Thursday");
        ls.add("Friday");
        ls.add("Saturday");
        ls.add("Sunday");
        String input = "";
        do {
            String day = sc.next();
            input+=day;
            System.out.println("输入:" + input);
            //存储周几的index
            List<Integer> indexList= new ArrayList<Integer>();
            for (int i = 0; i < ls.size(); i++) {
                Pattern p = Pattern.compile("^" + input.toLowerCase());
                Matcher m = p.matcher(ls.get(i).toLowerCase());
                boolean b = m.find(); // 是否找到以输入值开头的
                if (b) {
                    indexList.add(i);
                }
            }
            if (indexList.size() > 1) {
                System.out.println("您输入的可能是:");
                for (int i = 0; i < indexList.size(); i++) {
                    System.out.println(ls.get(indexList.get(i)));
                }
                System.out.println("请输入下一个字母");
            } else if (indexList.size() == 1) {
                System.out.println("输入的为:" + ls.get(indexList.get(0)));
                input = "";
            } else {
                System.out.println("识别不了您输入的是周几");
                input = "";
            }
        } while (true);
    }
}

源码