Question

这是我的代码的基础。它在控制台上打印学生成绩，但如何使用Buffereader将所有学生成绩放在新文件上。

import java.io.*;
import java.util.InputMismatchException;
import java.lang.*;
import java.util.*;

public class WorkSpace {

private Scanner x;

    public void openFile(){
        try{
            x = new Scanner (new File ("grades.txt"));
        }
        catch(Exception e){
            System.out.println("could not find file");
        }}



    public void createFile()throws IOException {


        try{
            File file = new File("grades.txt");
            Scanner s = new Scanner(file);




        while(s.hasNext()){
        {
            String [] split = s.nextLine().split(", ");

            String fname = split[0];

            Double q1 = Double.parseDouble (split[1]);
            Double q2 = Double.parseDouble (split[2]);
            Double q3 = Double.parseDouble (split[3]);
            Double q4 = Double.parseDouble (split[4]);
            Double proji = Double.parseDouble (split[5]);
            Double projii = Double.parseDouble (split[6]);
            Double projiii = Double.parseDouble (split[7]);

            double studentgrade = (q1 *0.1) + (q2 *0.1) +(q3 *0.1) + (q4 *0.1) +(proji*0.15) + (projii * 0.2) + (projiii *0.25);
            if(studentgrade>90)
                System.out.printf("%s got an A\n", fname);
            else if(studentgrade>80)
                System.out.printf("%s got a B\n", fname);
            else if(studentgrade>70)
                System.out.printf("%s got a C\n", fname);
            else if(studentgrade>60)
                System.out.printf("%s got a D\n", fname);
            else if(studentgrade>50)
                System.out.printf("%s got a F\n", fname);


        }}}catch(Exception e){
            e.printStackTrace();
        }



    }
    public void closeFile(){
        x.close();
    }

Answer 1

您如何阅读文件不正确。使用扫描仪读取文件的最常用方法：



try{
File file = new File("Your/File/Path");
Scanner s = new Scanner(file);
s.useDelimiter("\n");//splits the whole file's text by "\n"
while(s.hasNext()){
String next = s.next();
//parse your stuff
}
s.close();
}catch(Exception e){}

此外，

try{
File file = new File("Your/File/Path");
Scanner s = new Scanner(file);
s.useDelimiter("\n");//splits the whole file's text by "\n"
while(s.hasNext()){
String next = s.next();
//parse your stuff
}
s.close();
}catch(Exception e){}

不会返回文件的长度。那就是问题所在。使用scanner.nextInt()获取文件的长度。

Answer 2

Scanner.nextInt（）返回从源读取的下一个整数值（不是源长度或其他东西）。您打开文件并尝试在开头读取整数，但该文件不以整数开头，因此您将获得异常。

Answer 3

你的问题没有意义。 BufferedReader不会写文件。它，错误，读取文件。你想要的是，错误，BufferedWriter.

BufferReader用以前的信息写入新文件

3 个答案: