Java NullPointerException occurs when using scanner.hasNext();

I came up with the following code to read the information from the file:

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

public class Reader {

private Scanner s;

public void openFile() {
        try {
            s = new Scanner(new File("file.txt"));
        } catch (Exception e) {
            System.out.println("File not found. Try again.");
        }
    }

public void readFile() {
        while (s.hasNext()) {
            String a = s.next();
            String b = s.next();
            String c = s.next();
            int d = s.nextInt();
            int e = s.nextInt();
            int f = s.nextInt();
    }

public void closeFile() {
        s.close();
    }

}

However, I get a NullPointer error in the (while(s.hasNext())) line and can’t find a solution.

I’m working in Eclipse and the file I’m reading is properly imported into the project, so this shouldn’t be a problem.

Edit:

How I access the method:

public class Tester {

public static void main(String[] args) {

Reader read = new Reader();

read.openFile();
        read.readFile();
        read.closeFile();

}

}

According to the statement thrown by NPE, while (s.hasNext()), s is most likely a null pointer, you can add System.out.println(s); Double confirm the statement before it.

As for the reason why s is null, there are two possible causes:

1. You did not call openFile before readFile
2. An exception is thrown when opening a file. s is just a declaration and does not yet point to any object.

Perhaps for better practice, you can assert whether an instance is null or not before calling its methods. From what I understand, readFile depends on the result of openFile, maybe you can set the return value of openFile to a boolean value and check the return value before further open file operations. Files that can’t be read or even opened, right?

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

public class Reader {

private Scanner s;

public boolean openFile() {
        try {
            s = new Scanner(new File("file.txt"));
            return true;
        } catch (Exception e) {
            System.out.println("File not found. Try again.");
            return false;
        }
    }

public void readFile() {
        while (s.hasNext()) {
            String a = s.next();
            String b = s.next();
            String c = s.next();
            int d = s.nextInt();
            int e = s.nextInt();
            int f = s.nextInt();
     }
}

The caller can do the following:

Reader reader = new Reader();
if (reader.openFile())
    reader.readFile();