Java 输出错误的嵌套开关案例错误？

我的程序输出遇到一些问题。我确信这个错误是合乎逻辑的，但我就是修不好。错误应该在这附近的某个地方

 String plusorminus ="+-"; 

char mark = plusorminus.charAt(0);
char modifier = 0;

if(plusorminus.length() >= 1)
{
    modifier = plusorminus.charAt(1);
}

/*This is my utility scanner,
 * I created char grade to get the user input.
 */
java.util.Scanner input=new java.util.Scanner(System.in);
String userInputString = input.nextLine();
char grade = userInputString.charAt(0);

我不知道怎么修理它。目前，如果我在程序中插入A+，它将给出A-。这是我的全部代码

public class SwitchCase {

 public static void main(String[] args) {

System.out.println("Please enter your grade (ex.A+) to get the mark range");

/*This block of codes converts from string to
 * char and it gets the plus or minus sign
 */
String plusorminus ="+-"; 

char mark = plusorminus.charAt(0);
char modifier = 0;

if(plusorminus.length() >= 1)
{
    modifier = plusorminus.charAt(1);
}

/*This is my utility scanner,
 * I created char grade to get the user input.
 */
java.util.Scanner input=new java.util.Scanner(System.in);
String userInputString = input.nextLine();
char grade = userInputString.charAt(0);

/*This set of code contains the nested switch statements
 * that i will use to output the correct mark range
 * to the user. It also contains a try statement to find runtime
 * errors in the program.
 */
try{
switch(grade)
{
    case 'A':
        switch(modifier)
        {
            case '+': System.out.println("Your grade is 90-99.99%"); break;
            case '-': System.out.println("Your grade is 80-84.99%"); break;
            default: System.out.println("Your grade is 85-89.99%"); break;
        }
        break;
    case 'B':
        switch(modifier)
        {
           case'+': System.out.println("Your grade is 77.00 - 79.99%"); break;
           case'-': System.out.println("Your grade is 70.00 - 72.99%"); break;
           default: System.out.println("Your grade is 73.00 - 76.99%"); break;
        }
        break;   
    case 'C':
        switch(modifier)
         {
           case'+': System.out.println("Your grade range is 67.00 - 69.99%"); break;
           case'-': System.out.println("Your grade range is 60.00 - 62.99%"); break;
           default: System.out.println("Your grade range is 63.00 - 66.99%"); break;
         }
         break;
    case 'D':
         switch(modifier)
         {
           case'+': System.out.println("Your grade range is 55.00 - 59.99%"); break;
           case'-': System.out.println("-"); break;
           default: System.out.println("Your grade range is 50.00 - 54.99%"); break;
         }
         break;
    case 'F':
         switch(modifier)
         {
           default: System.out.println("Your grade range is 0.00-49.99%"); break;
          }    
         break;
        }
}
catch (java.util.InputMismatchException e) { //if the above error is met, message will be sent to the user
               System.out.println("Please enter a valid grade!");
         }
input.close(); //ends the user input
    }
}

之后

加

并删除处理加号或减号的代码

您还应该添加一些代码，以避免在读取输入行后出现打嗝

userInputString = userInputString.trim(); // maybe user hits space?
if( ! userInputString.matches( "^[A-F][-+]?$" ) ){
    // error message...
}

不确定是否有E和F+或F-？？我们有不同的等级。也许正则表达式应该是

"^[A-E][-+]?|F$"

---

您可能正在插入

A+

但是您只使用

A

String userInputString = input.nextLine();
char grade = userInputString.charAt(0);

修饰符

是在此处确定分配的

String plusorminus ="+-"; 

char mark = plusorminus.charAt(0);
char modifier = 0;

if(plusorminus.length() >= 1)
{
    modifier = plusorminus.charAt(1);
}

---

加号减号

的长度将始终为

2

，这意味着

修饰符

将始终为

加号减号.charAt（1）

，即

-

。您希望将输入字符串的第二个字符指定为

修饰符
什么是
修饰符=plusor减号.charAt（1）做什么？何时执行？是否没有“E”级？
String userInputString = input.nextLine();
char grade = userInputString.charAt(0);

String plusorminus ="+-"; 

char mark = plusorminus.charAt(0);
char modifier = 0;

if(plusorminus.length() >= 1)
{
    modifier = plusorminus.charAt(1);
}