java - While 循环创建永无止境的输入循环

Question

所以我希望我的程序读取输入“A”、“B”或“C”，并通过显示星号来显示每个输入的数量。但我遇到了一个问题，它从不读取和显示我的输入。

我的代码如下:

if (command == 'A'){
    System.out.println("Type the additional input in a single line.");
    while(in.hasNext()){
        String input = in.next().toUpperCase();
        if(input.equals("A")){ numA++;}
        if(input.equals("B")){ numB++;}
        if(input.equals("C")){ numC++;}
    }
    System.out.println("---------------------------------------");
    System.out.printf("\n%4s      |", "A");
    for (int a = 1; a <= numA; a++) { 
        System.out.print("*");
    }
    System.out.println();
    System.out.printf("\n%4s      |", "B");
    for (int b = 1; b <= numB; b++) {
        System.out.print("*");
    }
    System.out.println();
    System.out.printf("\n%4s      |", "C");
    for (int c = 1; c <= numC; c++) { 
        System.out.print("*");}
        System.out.println();
        double gpa = ((numA*4)+(numB*3)+(numC*2)) / ((numA+numB+numC));
        System.out.println("GPA: " + gpa);
        System.out.println();
        System.out.println("---------------------------------------");
    } 

Answer 1

意识到我错过了一个break语句。我的老师希望输入任何数字后都显示数据。 Break 语句是我以前从未了解或使用过的东西，但以下是我为感兴趣的人修复它的方法:

 if (command == 'A') {                                                               
     System.out.println("Type the additional input in a single line.");              
     while (in.hasNext()) {                                                          
         String input = in.next().toUpperCase();                                     
         if (input.equals("A")) {                                                    
             numA++;                                                                 
         }                                                                           
         if (input.equals("B")) {                                                    
             numB++;                                                                 
         }                                                                           
         if (input.equals("C")) {                                                    
             numC++;                                                                 
         }                                                                           
         if (input.compareTo("A") < 0 || input.compareTo("Z") > 0)                   
             break;                                                                  

     }                                                                               
     System.out.println("---------------------------------------");                  
     System.out.printf("\n%4s      |", "A");                                         
     for (int a = 1; a <= numA; a++) {                                               
         System.out.print("*");                                                      
     }                                                                               
     System.out.println();                                                           
     System.out.printf("\n%4s      |", "B");                                         
     for (int b = 1; b <= numB; b++) {                                               
         System.out.print("*");                                                      
     }                                                                               
     System.out.println();                                                           
     System.out.printf("\n%4s      |", "C");                                         
     for (int c = 1; c <= numC; c++) {                                               
         System.out.print("*");                                                      
     }                                                                               
     System.out.println();                                                           
     double gpa = ((numA * 4) + (numB * 3) + (numC * 2)) / ((numA + numB + numC));   
     System.out.println("GPA: " + gpa);                                              
     System.out.println();                                                           
     System.out.println("---------------------------------------");                  
 }                                                                                   

抱歉这个愚蠢的问题，我是java新手。