尝试使用 Integer.parseInt() 将字符串转换为整数时出错

Question

***更新我的帖子以显示我的所有代码，希望这能提供更多上下文。

当我运行程序时，它会跳过我的第一个“if”语句并引发错误。***

我收到错误Exception in thread "main" java.lang.NumberFormatException: For input string: ""

我正在尝试在 while 循环的第一个 else 语句中将字符串变量转换为 int...错误发生在 int examScore = Integer.parseInt(userInput).

   import java.util.Scanner;//imports scanner

   public class ExamScoresCalculator{

   public static void main(String[] args){



   Scanner scan = new Scanner(System.in);//creates new scanner object 

   //prompts user for lowest possible exam score
   System.out.println("Enter the lowest possible value for the exam: ");
   int lowRange = scan.nextInt();

   //prompts user for highest possible exam score
   System.out.println("Enter the highest possible value for the exam: ");
   int highRange = scan.nextInt();

   boolean flag = true; //while loop flag
   double lowestExamScore = highRange; // holds lowest score
   double highestExamScore = lowRange; //holds highest score
   double totalPoints = 0; //holds sum of all scores entered
   int totalExams = 0; //holds the total number of exams entered by the user

   while (flag == true){
      System.out.println("Enter an exam score between " + lowRange + " and " + highRange + " or type exit. "); //asks user for an exam score within correct range     
      String userInput = scan.nextLine();

      if ((userInput.equals("exit")) || (userInput.equals("Exit")) || (userInput.equals("EXIT"))){ //checks if user enters "exit"
         flag = false; //ends while loop

      }else{      
         int examScore = Integer.parseInt(userInput); //converts user input into integer 

         if (examScore >= lowRange && examScore <= highRange){ //checks if user entered a correct test score
            totalExams += 1; //increments totalExams by 1
            totalPoints += examScore; //adds examScore total to totalPoints

            if (examScore < lowestExamScore){ //checks if the exam score entered is the lowest 
               lowestExamScore = examScore; //updates lowestExamScore variable 
            }

            else if (examScore > highestExamScore){ //checks if exam score entered is the highest 
               highestExamScore = examScore; //updates highestExamScore variable 
            }

         }else{
            System.out.println("Please enter a correct score."); //asks user to enter a correct score 
         }

      }


   }//closing while loop 

   //prints the total number of exams, lowest score, highest score, and average score to screen 
   System.out.println("Total number of exams: " + totalExams);
   System.out.println("Lowest exam score: " + lowestExamScore);
   System.out.println("Highest exam score: " + highestExamScore);
   System.out.println("Average exam score: " + (totalPoints / totalExams)); 

   }//closing main 
   }//closing class

Answer 1

在您按下 ENTER 输入最高分数后，扫描仪会读取整数（nextInt）但也会读取行尾（nextLine）。由于在该行中没有提供文本，因此将其读取为空字符串“”。

您应该在代码中将scanner.nextInt 替换为scanner.nextLine。它应该可以在以下更改中正常工作。

//prompts user for lowest possible exam score
  System.out.println("Enter the lowest possible value for the exam: ");
   int lowRange = Integer.parseInt(scan.nextLine());

   //prompts user for highest possible exam score
System.out.println("Enter the highest possible value for the exam: ");
   int highRange = Integer.parseInt(scan.nextLine());

Answer 2

请为userInput 和examScore 使用两个输入，这将解决您的问题，因为您不能对String 和Integer 数据类型都使用一个值。

（但是当您的输入值为“123”（仅限数字）时，即使这也不适用于您的程序）

Answer 3

添加 scan.nextLine() 以移动扫描仪以读取下一行（新行）。

System.out.println("Enter the highest possible value for the exam: ");
int highRange = scan.nextInt();
scan.nextLine();   // Add this line