根据年月日计星期

public static void main(String[] args) {
        int y =2021; 
        int m =01;
        int d =21;
        System.out.println(caculateWeekDay(y, m, d));
    }
    
    private static  String  caculateWeekDay(int y, int m, int d) {
        if (m == 1) { m = 13; y--; }
        if (m == 2) { m = 14; y--; }
        int week = (d + 2 * m + 3 * (m + 1) / 5 + y + y / 4 - y / 100 + y / 400) % 7 + 1;
        String weekstr = "";
        switch (week)
        {
            case 1: weekstr = "星期一"; break;
            case 2: weekstr = "星期二"; break;
            case 3: weekstr = "星期三"; break;
            case 4: weekstr = "星期四"; break;
            case 5: weekstr = "星期五"; break;
            case 6: weekstr = "星期六"; break;
            case 7: weekstr = "星期日"; break;
        }
        return weekstr;
    }