如何在Java中从.txt文件提取信息？

Question

I currently have some code that can take console input, but I need to make it recognize a list of names and test scores. Code that I currently have:

import java.io.*;
import utils.io.*;

class student
{
   String name;
   double sResult[];
   int result;
   double sum;

   void getdata()
   {
      System.out.println("Enter name:");
      Name = (string) system.in.read();
      int index=0;

      for (int counter=1; counter<=5; counter++)
      {
         System.out.println("Enter result for subject"+counter+":");
         sResult[count] = (double) system.in.read();
      }
   }

   public static void CalculateAverage()
   {
      sum = 0;
      for (int i=1;i<=5;i++)
      {
         sum += sResult[i];
      }
      return (int) Math.round(sum/(values.length-1));
   }

   Public static char calculateGrade()
   {
      result=sum;
      if (result>=0 && result <=59)
      {
         return ('F');
      }
      else
      if (result >=60 && result<=69)
      {
         return ('E');
      }
      else
      if (result>=0 && result<79)
      {
         return ('D');
      }
      else
      if (result >=70 && result<=79)
      {
         return ('C');
      }
      else
      if (result>=80 && result<=89)
      {
         return ('B');
      }
      else
      if (result>=90 && result<=100)
      {
         return ('A');
      }
   }
}

and class test

public class test
{
   public static void main(String[] args)
{
   Student std;
   do
   {
      std=new Student();
      std.getdata();
      System.out.println("Student Name:"+std.Name);
      System.out.println("Average for"+std.Name+" "+"is:"+std.average());
      System.out.println("Grade for"+std.Name+" "+"is:"+std.gradecal());
      System.out.println("Want to continue (1-Yes,2-No");
   }
   while(System.in.read()==1);
}

The text document format is name score1 score2 score3 score4 score5

I only need help figuring out how to import the values, and then I can probably figure out how to rewrite the .txt using PrintWriter.

Thanks in advance for any help!

Answer 1

Firstly, you should not have variable names starting with a capital, namely:

string Name;

Only class names should start with a capital.

Also, I'm not even sure if your code compiles. Everywhere you have system.out.println should be System.out.println . Notice that System is a class, so the first letter is a capital

To read data, you can use BufferedReader and to write, you can use BufferedWriter . Usage:

BufferedReader in = new BufferedReader(new FileReader("FileName.txt"));
BufferedWriter out = new BufferedWriter(new FileWriter("OutputFileName.txt"));

in.readLine(); //This reads a single line from the text file
out.write("Your Output Text");
in.close(); // Closes the file input stream
out.close(); // Closes the file output stream

Since you are reading in the format:

name score1 score2 score3 score4 score5

you can use the some String functions to get each field.

String inputLine = in.readLine();
String [] fields = inputLine.split(" "); // Splits at the space
System.out.println(fields[0]); //prints out name
System.out.println(fields[1]); //print out score1
...

Answer 2

Here's how you do it with Scanner .

Scanner inputFile = new Scanner(new File("inputfile.txt"));
while(inputFile.hasNext()){ //if there is still something to read
     String name = inputFile.next();
     int score1 = inputFile.nextInt();    
     ....
     int score5 = inputFile.nextInt();
     //Do something here with the scores
     inputFile.next(); //Read the new line character and prepare for the next iteration 
}

For writing back to file, you can check Davy's answer and use a Buffered Writer. Note that the write() method works just like System.out.println() but you need to print \\n on your own to go to the new line.

Answer 3

public static void main(String... args) throws IOException {
    Scanner s = new Scanner(new BufferedReader(new FileReader("textfile.txt")));
    while(s.hasNext()){
        Student student = new Student(s.next(), s.nextDouble(), s.nextDouble(),
                                      s.nextDouble(), s.nextDouble(), s.nextDouble() ));
        // Do something with student
        s.next() // consume endline
    }
}