无法读取和存储文本文件中的每一行

Question

I have a text file named " math.txt " which has several math lines. These are the lines which are stored in math.txt .

1+2+3
1+2+3+4
1+2+3+4+5
1+2+3+4+5+6
1+2+3+4+5+6+7
1+2+3+4+5+6+7+8

I have the code below which is supposed to read out each line from the text file and then store each line in a String array. For some reason, only certain lines are printed, and only certain lines seem to be stored in the array.

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

class Main {
  public static void main(String[] args) throws IOException {

    //scanner which scans the text file with math equations
    Scanner file = new Scanner (new File("math.txt"));

    //new string array of of infinite size to read every line
    String [] lines = new String [100000];

    //int to count how many lines the text file has to be used in a future for loop
    int lineCount = -1;    


    System.out.println("\nPrint each line from text file");


    //if there is a line after the current line, the line count goes up and line is stored in the initial array
    while (file.hasNextLine()){
        System.out.println(file.nextLine());
        lineCount++;
        lines[lineCount] = file.nextLine();
    }

    System.out.println("\nLines in array");

    for(int i=0;i<lineCount; i++){
        System.out.println(lines[i]);
    }

  }
}

The output should be

Print each line from text file
1+2+3
1+2+3+4
1+2+3+4+5
1+2+3+4+5+6
1+2+3+4+5+6+7
1+2+3+4+5+6+7+8

Lines in array
1+2+3
1+2+3+4
1+2+3+4+5
1+2+3+4+5+6
1+2+3+4+5+6+7
1+2+3+4+5+6+7+8

But instead I get the output

Print each line from text file
1+2+3
1+2+3+4+5
1+2+3+4+5+6+7

Lines in array
1+2+3+4
1+2+3+4+5+6

Where is the issue in my code?

Answer 1

In your while loop:

while (file.hasNextLine()){
        System.out.println(file.nextLine());
        lineCount++;
        lines[lineCount] = file.nextLine();
    }

You are calling file.nextLine() twice. This means that lines are read twice for every storage. What you will need is something like this:

while( file.hasNextLine()) {
    String s = file.nextLine();
    System.out.println(s);
    lines[lineCount++] = s;
}

Also start your lineCount at 0 instead of -1;

Answer 2

Take a look at your while block:

while (file.hasNextLine()){
    System.out.println(file.nextLine());
    lineCount++;
    lines[lineCount] = file.nextLine();
}

Do you see that you use file.nextLine() twice? Each call to nextLine() advances the cursor, so while you intend to use the current line twice, the second call to nextLine() skips to the next line.

What you should do is store the line in a local field, and just use that field directly.

while (file.hasNextLine()){
    String foo = file.nextLine();
    System.out.println(foo);
    lineCount++;
    lines[lineCount] = foo;
}

Answer 3

The problem happens because you are reading 2 lines on every loop iteration. Every

file.nextLine()

is reading another line in the file.

You can try with this:

 while (file.hasNextLine()){
    lineCount++;
    lines[lineCount] = file.nextLine();
    System.out.println(lines[lineCount]);
 }