Exception in thread "main" java.lang.NullPointerException

[Rohaan]

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)

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(){
	
	}
}

What is causing this error?:confused:
Please help

[Fubarable]

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:

Scanner checker = new Scanner(findNoOfLines);

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:

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);
  }

}

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

for e.g.,

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);
    }
  }
}

Much luck!

[Rohaan]

Thankyou.
:)