java.util.InputMismatchException 输出错误

Question

我目前正在尝试从我的硬盘读取文件。文件名为“Sample.txt”，下面是我的代码。我能够编译并运行它，但收到此错误:

 Exception in thread "main" java.util.InputMismatchException
at java.util.Scanner.throwFor(Scanner.java:909)
at java.util.Scanner.next(Scanner.java:1530)
at java.util.Scanner.nextDouble(Scanner.java:2456)
at Proj1GradesService.errorReport(Proj1GradesService.java:42)
at Proj1GradesClient.main(Proj1GradesClient.java:13)

我试过只用 While 循环读取文件，现在用 try/catch 读取文件，但收到了同样的错误，我不确定它到底出了什么问题。我正在尝试从服务类读取文件并从客户端类调用方法 errorReport()。 任何帮助将不胜感激。

import java.util.*;   //allows use of Scanner class
import java.io.*;   //for File and IOException classes

class Proj1GradesService
{   //begin Proj1GradesService

  public void pageAndColHeading(char letter)   //accepts char as a parameter
  {   //start pageAndColHeading
     switch (letter)
     {   //start switch
        case 'e':   //write the caption for error report
           System.out.println ("Error Report - Students With Invalid GPA");   //prints Error Report
           break;

        case 'v':   //write the caption for valid report
           System.out.println ("Valid Report - Students With Valid");   //prints Valid Report
           break;
        default:  ;  //do nothing
     }//end switch
  }   //end pageAndColHeading

  public void errorReport() throws IOException
  {   //start errorReport

     Scanner scanFile = null;
     try
     {
        scanFile = new Scanner (new File ("p1SampleGPAData.txt"));
     }
        catch (FileNotFoundException fnfe)
        {
           System.out.println ("wrong file name."); 
        }   

     String name;   //name read from file
     double gpa;   //gpa read from file
     int count = 0;   //line #

     while (scanFile.hasNext( )) 
     {
        name = scanFile.next();
        gpa = scanFile.nextDouble();
        System.out.println ("Line Number: " + count + "Name: " + name + "GPA: " + gpa);

        ++count;
     }   //end while
     scanFile.close();

  }    //end errorReport


}   //end class

Answer 1

考虑下面从打印语句假定的文件结构

  name1 1.1
  name2 2.2
  name3 3.3

现在根据您的代码以下行

 // consume your whole line. ie name1 1.1
 name = scanFile.next(); 
 // looking for double but instead getting string ie name2
 // hence throwing InputMismatchException
 gpa = scanFile.nextDouble(); 

现在解决上述问题。您可以使用 String.split() .

  // collect whole line
  name = scanFile.next(); 

  // split by one or more whitespace OR use your delimiter 
  String[] str = name.split("\\s+");

  // gives name
  String actName = str[0];

  // gives gpa, throws NumberFormatException if str[1] is not double value
  double gpa = Double.parseDouble(str[1]);

希望对您有所帮助。如果您需要更多帮助，请直接提出。