Question

I have 2 files Details.java and TestDetails.java and a data file called Details.dat

Details.java

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

public class Details {
    private String path;
    File myFile = new File(path);

    public void setMyFile(String path) {
        this.path = path;

    }

    public void load() throws IOException, FileNotFoundException {
        Scanner input = new Scanner(myFile);

        int numberOfMembers = input.nextInt();

        String[] members = new String[numberOfMembers];

        for (String s : members) {

            String name = input.next();

            String age = input.next();

            String qualification = input.next();

            System.out.println("The name of the family member is " + name + " the age of the family member is" + age
                    + " the qualification of the " + "family member is" + qualification);

        }
    }
}

TestDetails.java

import java.io.IOException;

public class TestDetails {

    public static void main(String[] args) {

        Details myDetails = new Details();

        myDetails.setMyFile(args[0]);

        try {
            myDetails.load();
        } catch (IOException i) {

            System.out.println(i.getMessage());
        }
    }
}

Details.dat

4

a 26 bsc

b 22 bcom

c 50 ba

d 60 bsc

Whenever i try to run the TestDetails.java file i get a NullPointerException and the stack trace points the stack trace towards the File object.

So what is the problem here? Why am i getting a NullPointerException?

p.s in the setFile() method argumnet, i pass in Details.dat in the args[0] position on the command prompt

Answer 1

You initialize the File first and after that set the file path.
Try to use a constructor in the Details class:

public Details(String path)
        this.path = path;
        myFile = new File(path);
}