使用字符串进行切换时出错

Question

当我尝试使用字符串进行切换时收到错误消息。这是错误：

incompatible types found: 
java.lang.String 
required: int 
switch(monthName){

这使得我似乎只能使用 int 进行切换，但我很确定在较新的 Java 版本中，您可以使用 String 进行切换。这是给我错误的代码：

switch(monthName){
        case "December"://Always has 31 days
            daysLeft = 31;
            daysLeft -= dayOfMonth;
            break;
        case "November"://Always has 30 days
            daysLeft = 61;
            daysLeft -= dayOfMonth;
            break;
        case "October"://Always has 31 days
            daysLeft = 92;
            daysLeft -= dayOfMonth;
            break;
        case "September"://Always has 30 days
            daysLeft = 122;
            daysLeft -= dayOfMonth;
            break;

Answer 1

无法为低于 1.7 的源级别打开字符串类型的值。只允许可转换的 int 值或枚举常量

Answer 2

在你的类中定义枚举：

public enum MonthName {
    December, November, October, September
}

使用 val 变量提供基于字符串输入的开关功能-

String val = "December";//can be taken from user through Scanner class
MonthName monthName = MonthName.valueOf(val);//Enum class object

switch (monthName) {
    case December://Always has 31 days
        daysLeft = 31;
        daysLeft -= dayOfMonth;
        break;
    case November://Always has 30 days
        daysLeft = 61;
        daysLeft -= dayOfMonth;
        break;
    case October://Always has 31 days
        daysLeft = 92;
        daysLeft -= dayOfMonth;
        break;
    case September://Always has 30 days
        daysLeft = 122;
        daysLeft -= dayOfMonth;
        break;
    }
    System.out.println(dayOfMonth + "---" + daysLeft);//Test of output
}