Yet another java.lang.NullPointerException - while using the Writer

[Tellier]

I'm quite new to the world of Java development and after struggling with different projects I decided to actually complete an "advanced" (for me) program. While playing around with the Writer.class and storing information in .txt files I came across the java.lang.NullPointerException. I've read some other threads about the subject but I can't find the solution to my own problem.

The only thing that I know is that I know is that, after running the program once and storing 2 lines of information I get an error when I start the program again and try to add more lines of text. I've fail searched my vector and when it doesn't contain any information even though it returns 2 when I do person.size().

Edit: Forgot to mention the specific Exception, here we go:

Exception in thread "main" java.lang.NullPointerException
at java.io.Writer.write(Writer.java:157)
at name.and.age.Register.inputWriter(Register.java:47 )
at name.and.age.Register.main(Register.java:90)
Java Result: 1
BUILD SUCCESSFUL (total time: 4 seconds)

Some help would be much appreciated!

Hint: I know that the actual code is a mess, but I'll take care of that later (but constructive feedback is always good)

package name.and.age;

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

public class Register {
    
    static Scanner sc = new Scanner(System.in);
    public static final Vector<String> person = new Vector<String>();
    
    public void StartProgram() {
        try{
            FileReader fr = new FileReader("Register.txt");
            BufferedReader br = new BufferedReader(fr);
        
            int lineNumber = 0;
            while(br.readLine() != null){
            lineNumber++;
            }
            for(int i = 0; i < lineNumber; i++){
                person.add(br.readLine());
            }
            fr.close();
        } catch(IOException ioe){
            //ignore problem
        }
        
    }
    
    public void inputWriter() {
        try {
            FileWriter fw = new FileWriter("Register.txt");
            BufferedWriter bw = new BufferedWriter(fw);

            String inputName;
            String inputAge;
        
            System.out.println("Enter the name of the person: ");
            inputName = sc.next();
            System.out.println("");
            System.out.println("Enter the age of the person: ");
            inputAge = sc.next();
        
            person.add(inputName + " " + inputAge + "\r");

            for(int i = 0; i < person.size(); i++){
                bw.write(person.get(i));
            }
        
            bw.close();
            fw = null;
            
        } catch(IOException e){
            //ignore problem
        }
    } 
    
    public void filePrint() {
        try{
            FileReader fr = new FileReader("Register.txt");
            BufferedReader br = new BufferedReader(fr);
            
            String s;
            while((s = br.readLine()) != null){
                System.out.println(s);
            }
        } catch(IOException e){
            System.out.println("Error! ");
        }
    }
    
    public static void main(String[] args) throws Exception{
        
        Register yes = new Register();
        yes.StartProgram();
        int choice;
        
        do{
            System.out.println ("");
            System.out.println ("1. Add a new person");
            System.out.println ("2. List all the people!");
            System.out.println ("3. Exit program");
            System.out.println ("");
            System.out.print("Your choice: ");
            choice = sc.nextInt();
            System.out.println("");
        
        
            if(choice == 1){
                yes.inputWriter();
            } else if(choice == 2){
                yes.filePrint();
            } else if(choice == 3){
                System.out.println ("Bye!");
            } else {
                System.out.println ("Wrong input!");
            } 
        } while(choice != 3);
        
    }
}

[Tolls]

Supply the full error text and stack trace, highlighting the line in your code on which the exception occurs.

This will involve changing your exception handling to <exception>.printStackTrace().

[Tellier]

Thank you! I actually tried another solution that I while searching on google which took care of problem:

I removed line 46-48 and changed the FileWriter in inputWriter() to

FileWriter fw = new FileWriter("Register.txt", true);

In order to add new names I just wrote

bw.write(inputName + " " + inputAge + "\r");

and it took care of the problem... so far.