如何使用I / O打印带有文件号的txt文件？

Question

i am printing a .txt file using the Scanner and I want to print the file with line numbers. here is my code. My problem is that the line numbers aren't incrementing.

import java.util.*;
import java.io.*;


public class List 
{
  public static void main(String[] args) throws IOException
  {
    int line =1;
    File f = new File("src/List.txt");


    Scanner sc = new Scanner(f);
    while(sc.hasNext())
    {
        int num = 1;
        System.out.print(num);
        System.out.println(sc.nextLine());
        num++;
    }
  }
}

Output:

1Bird
1Dog
1Cat
1Elephant
1Tiger
1Zebra

Expected Output:

1 Bird
2 Dog
3 Cat
4 Elephant
5 Tiger
6 Zebra

Answer 1

Take int num = 1 and place it out side of the loop...

int num = 1;
while(sc.hasNext())
{
    System.out.print(num);
    System.out.print(" "); // Separate the line number from the text
    System.out.println(sc.nextLine());
    num++;
}

This way it won't be reset every time the loop restarts...

Answer 2

Your bug seems to be mixing up line and num in the body of the loop, but I would also recommend you use formatted output and something like -

while(sc.hasNextLine()) {
  System.out.printf("%d %s%n", line++, sc.nextLine());
}

The format String "%d %s%n" describes a number then a space then a String and then new-line. Next, perform a post-increment on line . Finally, get the nextLine() from the Scanner .

Answer 3

You should remove

int num = 1;

because this will ALWAYS set num BACK TO 1 while it hasNext. This is why the line number won't increment.

After deleting that, also delete

num++;

because there is no more num variable. Replace that with:

line++;

I hope this helps!