NullPointerException Error when Reading an Array Element from a File - Java

Question

In my program, I create an attraction and fill out the number of ticket types, is title and cost, and then I exit the program and run it again.

I have a constructor that reads elements from a file. When I then try to read an array element, it gives me a NullPointerException error even though the element is not null.

When I comment out the code block below where the error is located, I get a NumberFormatException error instead for the input string, "Tour Only", so I know it's not null.

fileScanner.nextLine();
for (int i = 0; i < getTicketTypesNum(); i++)
    this.ticketTypeTitle[i] = fileScanner.nextLine();
fileScanner.nextLine();

The code in full is below.

Attraction.java

// The constructor.
public Attraction(Scanner fileScanner) {
  ...

  // The data read before the error.
  fileScanner.nextLine();
  this.ticketTypesNum = Integer.parseInt(fileScanner.nextLine());
  fileScanner.nextLine();

  fileScanner.nextLine();
  for (int i = 0; i < getTicketTypesNum(); i++) {
    // Line where the error is located.
    this.ticketTypeTitle[i] = fileScanner.nextLine();
  }

  fileScanner.nextLine();
  for (int i = 0; i < getTicketTypesNum(); i++)
     this.ticketTypeCost[i] = Integer.parseInt(fileScanner.nextLine());
  fileScanner.nextLine();

  ...
}


// Store the attraction information and write it to file.
public void writeData(PrintWriter pw) {
  ...

  pw.println("Number of Ticket Types:");
  pw.println(getTicketTypesNum());
  pw.println();

  pw.println("Ticket Titles:");
  for (int i = 0; i < getTicketTypesNum(); i++)
    pw.println(getTicketTypeTitle()[i]);
  pw.println();

  pw.println("Ticket Costs:");
  for (int i = 0; i < getTicketTypesNum(); i++)
    pw.println(getTicketTypeCost()[i]);
  pw.println();

  ...
}

If you need more code, I'll edit my question to include more.

Thank you for your help!

UPDATE

I tried commenting out the line where I had the error out and continued running the code, and I get a NullPointerException whenver I have to read an array element.

So the array is not initialised? Did you try to use the debugger? — Joakim Danielson, May 24 '20 at 07:12

score 0 · Answer 1 · answered May 24 '20 at 07:17

0

You shoul check fileScanner.hasNextLine() before using fileScanner.nextLine()

answered May 24 '20 at 07:17

Hayrettin Çetintaş

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1
1
11

I have a while check elsewhere that checks that. – Wolfizzy May 24 '20 at 07:25
You should check before everytime you want to use. – Hayrettin Çetintaş May 24 '20 at 07:28
Could you tell me why you are using fileScanner.nextLine(); before and after for loop? – Hayrettin Çetintaş May 24 '20 at 07:30

score 0 · Accepted Answer · answered May 24 '20 at 07:29

This is the sample program which works. You can try this and print your array. Make sure you have this scanner.hasNextLine() check before getting the elements from file. Also, ideally your array size should be equal to number of occupied lines in file.

import java.io.File;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.Scanner;

public class FileRead {

    public static void main(String args[]) {

        String array[] = new String[6];

        File file = new File("C:\\Users\\Desktop\\text");

        try (Scanner sc = new Scanner(file, StandardCharsets.UTF_8.name())) {
            int i =0;
            while (sc.hasNextLine()) {

                array[i] = sc.nextLine();
                i++;
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        System.out.println(Arrays.toString(array));

    }

}

Let me know if this works for you.

Thank you @TanviGarg! I didn't allocate memory, so that's why it didn't work. — Wolfizzy, May 24 '20 at 07:43

NullPointerException Error when Reading an Array Element from a File - Java

2 Answers2