java - 每次我编译项目时，while 循环之外的所有内容都不会显示(输入来自文件)

Question

import java.io.*;
import java.util.*;
public class Statistics {

    public static void main(String[] args) throws IOException {
        Scanner in = new Scanner(new FileReader("C:\\Users\\user\\Desktop\\students.dat"));//Opened file

        int math=0,spanish=0,french=0,english=0,count=0,sum,highSpan=0,highMath=0,highFren=0,highEng=0;//Declarations
        double avg,highAvg=0;
        String name,highName;
        highName="";
        name = "";                      //Prime read
            while (name!="ENDDATA"){        //Sentinel condition
                count++;                    //Keeps count of students
                name = in.next();
                spanish=in.nextInt();
                math=in.nextInt();
                french=in.nextInt();
                english=in.nextInt();
                sum = spanish + math + french + english;
                avg = sum/4;                                    //Claculates Average
                System.out.printf("%s - %.0f\n",name,avg);

                    if (avg > highAvg){                         //Checks for the highest Average
                        highAvg = avg;
                        highName = name;
                    }
                    if (spanish > highSpan){
                        highSpan = spanish;
                    }
                    if (math > highMath){
                        highMath = math;                        //Checks for the highest mark for each subject
                    }
                    if (french > highFren){
                        highFren = french;
                    }
                    if (english > highEng){
                        highEng = english;
                    }

                name = in.nextLine();
            }

        System.out.printf("Number of students in class is: %d\n",count);
        System.out.printf("The highest student average is: %f\n",highAvg);
        System.out.printf("The student who made the highest average is: %s\n",highName);
        System.out.printf("The highest Spanish mark is: %d\n",highSpan);
        System.out.printf("The highest Math mark is: %d\n",highMath);
        System.out.printf("The highest French mark is: %d\n",highFren);
        System.out.printf("The highest English mark is: %d\n",highEng);
        in.close();                                                                 //Closing of file
    }
} 

编写一个Java程序来读取和处理文本文件的每一行并打印以下内容信息(除了最后一行之外的每一行):类(class)学生人数每个学生的姓名和平均分类(class)中最高的学生平均分(忽略平局的可能性)平均分最高的学生姓名(忽略平局的可能性)每个科目的最高分

它应该从 dat 文件中读取数据并进行必要的输出，但是 while 循环之外的打印语句没有显示，我也得到了带有以下错误的输出。

MARY - 65
SHELLY - 70
JOHN - 60
ALFRED - 71
Exception in thread "main" java.util.NoSuchElementException
    at java.util.Scanner.throwFor(Scanner.java:862)
    at java.util.Scanner.next(Scanner.java:1485)
    at java.util.Scanner.nextInt(Scanner.java:2117)
    at java.util.Scanner.nextInt(Scanner.java:2076)
    at Statistics.main(Statistics.java:17)

Answer 1

in.nextInt() 抛出 NoSuchElementException。

您的文件似乎包含不正确的数据。

你的 while 循环永远不会中断，因为你的条件:

   while(name!="ENDDATA")

永远都是真的。这就是为什么当所有 token 都用完时，扫描仪对象会抛出 NoSuchElementException。并且由于出现异常，因此 while 循环之后的 print 语句不会被执行。

尝试使用扫描器的hasNext()方法来检查下一个 token 。

用这个 while 替换你的 while 循环。

  while (in.hasNext()){        //Sentinel condition
            count++;                    //Keeps count of students
            name = in.next();
            if(name.equals("ENDDATA")){
               break;
            }
            spanish=in.nextInt();
            math=in.nextInt();
            french=in.nextInt();
            english=in.nextInt();
            sum = spanish + math + french + english;
            avg = sum/4;                                    //Claculates Average
            System.out.printf("%s - %.0f\n",name,avg);

                if (avg > highAvg){                         //Checks for the highest Average
                    highAvg = avg;
                    highName = name;
                }
                if (spanish > highSpan){
                    highSpan = spanish;
                }
                if (math > highMath){
                    highMath = math;                        //Checks for the highest mark for each subject
                }
                if (french > highFren){
                    highFren = french;
                }
                if (english > highEng){
                    highEng = english;
                }


 }

Students.dat 文件格式应如下所示:

Shelly 2 2 3 4
Brown 34 2 1 4
Pink 23 45 21 1
ENDDATA