在Java中读取和写入.txt文件 [英] Reading and Writing to a .txt file in Java

问题描述

以下是我的分配提示：
您的程序需要从文本文件中读取信息，而不是使用扫描程序从命令行读取。
您的程序还需要将消息写入文本文件，而不是在屏幕上显示消息。

我已编写并运行代码以提示使用CLI。但是，我完全不知道如何使用文本文件更改代码。有人可以向我解释一下吗？

到目前为止的代码：

  import java.util。*; 
 
 public class parallelArrays {
 
 public static void main（String [] args）{
 String [] names; 
 int [] exam1Grades; 
 int [] exam2Grades; 
 int n，sum1，sum2; 
 double avg1，avg2; 
 
 Scanner kb = new Scanner（System.in）; 
 
 //从用户那里获取学生人数
 System.out.print（输入学生人数：）; 
 n = kb.nextInt（）; 
 
 //分配数组
 names = new String [n]; 
 exam1Grades = new int [n]; 
 exam2Grades = new int [n]; 
 
 //输入名称和等级
 for（int i = 0; i< = names.length-1; i ++）{
 System.out.print（Enter学生姓名＃+（i + 1）+：）; 
 names [i] = kb.next（）; 
 System.out.print（输入考试＃1年级：）; 
 exam1Grades [i] = kb.nextInt（）; 
 System.out.print（输入考试＃2等级：）; 
 exam2Grades [i] = kb.nextInt（）; 
} 
 
 //加起所有等级（可以在上面的循环中完成）
 sum1 = 0; 
 sum2 = 0; 
 for（int i = 0; i< = names.length-1; i ++）{
 sum1 = sum1 + exam1Grades [i]; 
 sum2 = sum2 + exam2Grades [i]; 
} 
 
 //计算并输出平均值
 avg1 = sum1 / n; 
 System.out.println（）; 
 System.out.println（考试＃1平均：+ avg1）; 
 
 avg2 = sum2 / n; 
 System.out.println（考试＃2平均：+ avg2）; 
 System.out.println（）; 
 
 //将每个等级与平均
进行比较（int i = 0; i< = names.length-1; i ++）{
 if（exam1Grades [i]> ; avg1）
 System.out.println（学生+姓名[i] +在考试1中高于平均水平）; 
 else if（exam1Grades [i]< avg1）
 System.out.println（Student+ names [i] +低于考试1的平均值）; 
 else 
 System.out.println（Student+ names [i] +是考试1中的平均值）; 
 
 if（exam2Grades [i]> avg2）
 System.out.println（Student+ names [i] +在考试2中高于平均水平）; 
 else if（exam2Grades [i]< avg2）
 System.out.println（Student+ names [i] +低于考试2的平均值）; 
 else 
 System.out.println（Student+ names [i] +是考试2中的平均值）; 
 
} 
} 
} 
  

解决像@Shobit先前所说的那样，将BufferedWriter与FileWriter一起使用，并使用write（）和newLine（）方法，您可以将所需的行插入文件而不是使用Println。 / p>

  BufferedWriter writer = new BufferedWriter（new FileWriter（path-of-file））; //你不需要创建一个File对象，FileWriter也为文件路径获取一个字符串以及
 writer.write（Student number ...）; 
 writer.writeLine（）; //对于文件中的新行
  

当你写完文件后，

  writer.close（）; 
  

Here is my prompt for the assignment: Your program needs to read the information from a text file instead of using a scanner to read from command line. Your program also needs to write the messages into a text file instead of showing the messages on the screen.

I have the code written and running for it to prompt using the CLI. However, I have absolutely no idea how to change the code utilizing a text file. Can someone please explain this to me?

Code so far:

import java.util.*;

public class parallelArrays {

    public static void main(String[] args) {
       String[] names;
       int[] exam1Grades;
       int[] exam2Grades;
       int n, sum1, sum2;
       double avg1,avg2;

       Scanner kb = new Scanner(System.in);

       // Get the number of students from the user
       System.out.print("Enter # of students:");
       n = kb.nextInt();

       // Allocate the arrays
       names = new String[n];
       exam1Grades = new int[n];
       exam2Grades = new int[n];

       // Input the names and grades
       for (int i=0; i<=names.length-1; i++) {
          System.out.print("Enter name for student #" + (i+1) + ":");
          names[i] = kb.next();
          System.out.print("Enter exam #1 grade:");
          exam1Grades[i] = kb.nextInt();
          System.out.print("Enter exam #2 grade:");
          exam2Grades[i] = kb.nextInt();
       }

       // Add up all the grades (could have been done in the above loop)
       sum1 = 0;
       sum2 = 0;
       for (int i=0; i<=names.length-1; i++) {
          sum1 = sum1 + exam1Grades[i];
          sum2 = sum2 + exam2Grades[i];
       }

       // Calculate and output the averages
       avg1 = sum1/n;
       System.out.println();
       System.out.println("Exam #1 average: " + avg1);

       avg2 = sum2/n;
       System.out.println("Exam #2 average: " + avg2);
       System.out.println();

       // Compare each grade to the average
       for (int i=0; i<=names.length-1; i++) {
       if (exam1Grades[i] > avg1)
           System.out.println("Student " + names[i] + " is above average on exam 1");
           else if (exam1Grades[i] < avg1)
           System.out.println("Student " + names[i] + " is below average on exam 1");
           else
           System.out.println("Student " + names[i] + " is average on exam 1");

       if (exam2Grades[i] > avg2)
           System.out.println("Student " + names[i] + " is above average on exam 2");
           else if (exam2Grades[i] < avg2)
           System.out.println("Student " + names[i] + " is below average on exam 2");
           else
           System.out.println("Student " + names[i] + " is average on exam 2");

       }
    }
}

解决方案

like @Shobit said previously, use a BufferedWriter in conjunction with a FileWriter and with the methods write() and newLine() you can insert the lines you want to the file in stead of using Println.

BufferedWriter writer = new BufferedWriter(new FileWriter("path-of-file")); //you don't need to create a File object, FileWriter takes a string for the filepath as well
writer.write("Student number..."); 
writer.writeLine(); //for a new line in the file

and when you are done writing to the file,

writer.close();

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