Exception in thread "main" java.lang.NullPointerException

Hi
whenever I try to compile and run the following code, i get this error
Exception in thread "main" java.lang.NullPointerException
at java.io.FileInputStream.<init>(Unknown Source)
at java.util.Scanner.<init>(Unknown Source)
at animalmain.main(animalmain.java:24)

Code:

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import java.util.Scanner;
import javax.swing.*;


public class animalmain {


        public static void main(String[] args) throws Exception {
               
       
                int noOfLines = 0;
                int b = 1;
                int ask;
                boolean win = false;
                String lineSeparator = System.getProperty("line.separator");
               
                JFileChooser filechooser = new JFileChooser();
               
                java.io.File findNoOfLines = filechooser.getSelectedFile();
                Scanner checker = new Scanner(findNoOfLines);               
                checker.useDelimiter(lineSeparator);
                while (checker.hasNext()){
                        noOfLines++;
                }
       
            checker.close();
       
       
       
       
    questionarray[]quest = new questionarray[noOfLines];
        for(int i = 0; i < quest.length; i++){
                quest[i] = new questionarray();
        }
               
                java.io.File file = filechooser.getSelectedFile();
                Scanner reader = new Scanner(file);
                reader.useDelimiter("|");
                while (reader.hasNext()){
                int i = reader.nextInt();
                quest[i].q = reader.next();
                quest[i].yes = reader.nextInt();
                quest[i].no = reader.nextInt();
                }
               
                reader.close();
               
       
                while (b <= quest.length){
                        ask = JOptionPane.showConfirmDialog(null,
                                        quest[b].q,
                                        "Guess  1.0",
                                        JOptionPane.QUESTION_MESSAGE);
                        if (ask == JOptionPane.YES_OPTION)
                                b = quest[b].yes;
                       
                        else
                                b = quest[b].no;
                       
                        if(b == -1){
                          win = true;
                          break;
                        }
                        else if (b == -2){
                          win = false;
                          break;
                        }
                }
               
               
                if (win == true){
                        JOptionPane.showMessageDialog(null, "I win");
                }
                else if (win == false){
                        java.io.PrintWriter toFile = new java.io.PrintWriter(file);
                        Scanner writeToFile = new Scanner(file);
                        String write = JOptionPane.showInputDialog("Enter the animal you were thinking of");
                        String writer = JOptionPane.showInputDialog("Enter a question that you could answer yes for " + write + " and no for " + quest[b].q);
                       
                        while (writeToFile.hasNext()){
                        String s1 = writeToFile.nextLine();
                        String s2 = s1.replaceAll(quest[b].q + writeToFile.nextInt() + writeToFile.nextInt(), writer + (quest.length+1) + (quest.length+2) );
                       
                }
                        toFile.print((quest.length+1) + "|" + quest[b].q + "|");
                        toFile.print(-1);
                        toFile.print("|");
                        toFile.println(-2);
                }       
               
               
        }

}
class questionarray{
        int qnum;
        String q;
        int yes;
        int no;
        questionarray(){
       
        }
}

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What is causing this error?:confused:
Please help

The NullPointerException (NPE) tells you which line is null, and so you know where to look for the problem. I can tell you that it will trip here:

Code:

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Scanner checker = new Scanner(findNoOfLines);

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and since checker can't be null, it must be findNoOfLines. This is most certainly null since you're asking the JFileChooser object to return a file before you've even displayed it.

To prove the point, run this:

Code:

---

import javax.swing.*;

public class Fu2 {

  public static void main(String[] args) throws Exception {
    JFileChooser filechooser = new JFileChooser();
    java.io.File findNoOfLines = filechooser.getSelectedFile();
    //Scanner checker = new Scanner(findNoOfLines);
    System.out.println(findNoOfLines);
  }

}

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I suggest that you read the JFileChooser API and tutorial to see how to display it and use it.

for e.g.,

Code:

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import javax.swing.*;

public class Fu2 {

  public static void main(String[] args) throws Exception {
    JFileChooser filechooser = new JFileChooser();
    int result = filechooser.showOpenDialog(null);
    if (result == JFileChooser.APPROVE_OPTION) {
      java.io.File findNoOfLines = filechooser.getSelectedFile();
      System.out.println(findNoOfLines);
    }
  }
}

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Much luck!

Thankyou.
:)