无法从RandomAccessFile Java获得正确的输出

Question

So here is the code that I ran.

import java.io.*;
public class SETBQ1 {
  public static void main(String[] args) throws Exception {
    RandomAccessFile item = new RandomAccessFile("item.dat", "rw");
    String s;
    while ((s = item.readLine()) != null) {
      System.out.println(s);
    }
    System.out.println(s);
    item.close();
  }
}

By the way, the contents of item.dat are

1 pencil 100 10
2 pen 200 5
3 eraser 5 1000
4 book 500 12

However, the output I am getting is

PS F:\tymalik\Malik\SEM 1\JAVA\ASS5> java SETBQ1
1 pencil 100 10
2 pen 200 5
3 eraser 5 1000
4 book 500 12
null

I would like to know why that last value prints null instead of a value? and what would be the solution to process the string variable outside of the while loop? I would appreciate any help on this one.

Answer 1

The last statement

System.out.println(s);

displays null since it is outside the scope of the while loop. You could assign another variable within the loop instead

String lastLine = null;
while ((s = item.readLine()) != null) {
    System.out.println(s);
    lastLine = s;
}
System.out.println(lastLine);