Exception in thread "main" java.lang.NullPointerException Read element from txt

Question

I am a beginner in java programming. I am trying to develop a program but when I ran my program which is posted below and it came back with this error:

Exception in thread "main" java.lang.NullPointerException
    at ChargeAccount1.isValid(ChargeAccount1.java:39)
    at ChargeAccount1Test.main(ChargeAccount1Test.java:22)

Here is my code:

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

public class ChargeAccount1 {

 private  int [] valid;

    public void main(String[] args) throws IOException {
         FileReader file = new FileReader("Account.txt");

        valid=new int [10];
        int i=1;

            Scanner input = new Scanner(file);
            while(input.hasNext())
            {
                valid[i] = input.nextInt();
                i++;
            }
            input.close();

        }


    public boolean isValid(int number) {
        boolean found = false;
        int n = 0;
        while (!found && n < valid.length) {
            if (valid[n] == number) {
                found = true;
            } else {
                n++;
            }
        }
        return found;
    }
}
public class ChargeAccount1Test {
   public static void main(String[]args)throws IOException{
        ChargeAccount1 in = new ChargeAccount1();
        Scanner scan = new Scanner(System.in);
        System.out.println("Please enter a charge account number:");
        String account = scan.nextLine();
        int number = Integer.parseInt(account);
        if (in.isValid(number)) {
            System.out.println("This is a valid account number");
        } else {
            System.out.println("This is an invalid account number");
        }
   }
}

would you please mark the line with the exception, we don't have line numbers... — PrR3
– PrR3, Commented Mar 3, 2014 at 15:17
Don't expect the main of ChargeAccount1 to be executed, since not the root of the program. Indeed, ChargeAccount1Test is the root. — Mik378
– Mik378, Commented Mar 3, 2014 at 15:18

nikis · Accepted Answer · 2014-03-03 15:23:20Z

2

Your valid is null. main method is not a constructor, it's just an top-level entry point point. So when you make a call in.isValid(number), valid inside your object is null since you initialize it only at the main method and that's why you may want to call in.main(null) at first.

edited Mar 3, 2014 at 15:23

answered Mar 3, 2014 at 15:17

nikis

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