在java中执行switch语句时,对象不会更新

String day = "Monday";

switch (day) {
    case "Monday":
        System.out.println("今天是星期一");
        break;
    case "Tuesday":
        System.out.println("今天是星期二");
        break;
    case "Wednesday":
        System.out.println("今天是星期三");
        break;
    case "Thursday":
        System.out.println("今天是星期四");
        break;
    case "Friday":
        System.out.println("今天是星期五");
        break;
    case "Saturday":
        System.out.println("今天是星期六");
        break;
    case "Sunday":
        System.out.println("今天是星期日");
        break;
    default:
        System.out.println("输入的日期不正确");
        break;
}

String day = "Monday";

switch (day) {
    case "Monday":
        day = "星期一";
        System.out.println(day);
        break;
    case "Tuesday":
        day = "星期二";
        System.out.println(day);
        break;
    case "Wednesday":
        day = "星期三";
        System.out.println(day);
        break;
    case "Thursday":
        day = "星期四";
        System.out.println(day);
        break;
    case "Friday":
        day = "星期五";
        System.out.println(day);
        break;
    case "Saturday":
        day = "星期六";
        System.out.println(day);
        break;
    case "Sunday":
        day = "星期日";
        System.out.println(day);
        break;
    default:
        System.out.println("输入的日期不正确");
        break;
}