Thread: reading files

import java.io.*;
import java.util.Formatter;
import java.util.Scanner;
import java.util.Vector;
 
public class read_file 
{
	private Formatter make_file;
	private Vector<String>names;
	private int counter;
	private Vector<Integer>age;
 
	void FileInput()
	{
		File input = new File("example.txt");
 
		if(!input.exists())
		{
			try{make_file = new Formatter("example.txt");System.out.println("A file had to be made, named "+input);}
			catch(IOException e){System.out.println("File was unable to be made");}
		}
		else
		{
			try 
			{
			Scanner reader = new Scanner(new FileInputStream(input));
 
			while(reader.hasNext())
			{
				names.add(reader.nextLine());
				age.add(reader.nextInt());
				counter++;	
			}
 
			}catch(Exception e){System.out.println("The file could not be read");}
		}
	}
 
	void PrintFile()
	{
 
		for(int i=0;i<counter;i++){System.out.println(names.get(i)+" "+age.get(i));}
	}
 
	public static void main(String[] args)
	{
		read_file r = new read_file();
 
		r.FileInput();
		r.PrintFile();
 
	}
 
}

I am playing with different way to take input from file it is not working.

}catch(Exception e){System.out.println("The file could not be read");}

keeps popping up. The file is being created though. Is a vector a good way to handle this? I read some bad things about vectors in Java but I used them all the time in C++. What is the deal with that?

The files look like:

name age
name age
name age
etc........

java.lang.NullPointerException
at read_file.FileInput(read_file.java:30)
at read_file.main(read_file.java:49)

NULL??? I didn't even push anything into the vector... Do I need to create the Vector again "new"? I tried to do that and I got a bunch of errors.

I know that but why would I initialize a vector. I used it because it is flexible and can grow in size as I wish. If not I would have made an array. I am beginning to think Vectors work differently in Java then C++.

A Vector is an object like any other. All objects must be initialized before you use them, there are no exceptions.

By the way, Vector is a very old and outdated class. A better choice is the ArrayList class.

Ahhhh arrayList, never heard of this before. I will use this, thanks. So I must do something like ArrayList<String> list = new ArrayList<String>(); before I can use it?

Originally Posted by jocdrew21

Ahhhh arrayList, never heard of this before. I will use this, thanks. So I must do something like ArrayList<String> list = new ArrayList<String>(); before I can use it?

This would be better coding practice as some might say:

List<String> someList = new ArrayList<>();

import java.io.*;
import java.util.ArrayList;
import java.util.Formatter;
import java.util.List;
import java.util.Scanner;
 
 
public class read_file 
{
	private Formatter make_file;
	private ArrayList<String>names;
	private int counter;
	private ArrayList<Integer>age;
 
	// error saysjava.lang.NullPointerException, java.lang.NullPointerException
	//at read_file.FileInput(read_file.java:37)
	//at read_file.main(read_file.java:56)
 
	//tried to make a constructor and create new string objects but this doesn't work either.
	public read_file(){/*names = new ArrayList<String>(); age= new ArrayList<Integer>();*/} 
 
	void FileInput()
	{
		File input = new File("example.txt");
 
		if(!input.exists())
		{
			try{make_file = new Formatter("example.txt");System.out.println("A file had to be made, named "+input);}
			catch(IOException e){System.out.println("File was unable to be made");}
		}
		else
		{
			try 
			{
			Scanner reader = new Scanner(new FileInputStream(input));
 
			while(reader.hasNextLine())
			{
 
				names.add(reader.nextLine());
				age.add(reader.nextInt());
				counter++;	
			}
			reader.close();
			}catch(Exception e){System.out.println("The file could not be read "+e);e.printStackTrace();}
		}
	}
 
	void PrintFile()
	{
 
		for(int i=0;i<counter;i++){System.out.println(names.get(i)+" "+age.get(i));}
	}
 
	public static void main(String[] args)
	{
		read_file r = new read_file();
 
		r.FileInput();
		r.PrintFile();
	}
}

I am still having issues with this code. I am trying to learn more about file handling but keep getting this error. I stopped using vectors and am now using ArrayList and from what I have read it is a linked list right?

java.lang.NullPointerException
java.lang.NullPointerException
at read_file.FileInput(read_file.java:37)
at read_file.main(read_file.java:56)

public read_file(){names=null;age=null; }

That is what I am trying to do. I do not know what the heck is going on.

The issue is on line 38 like the error says.
I was not getting any errors until I put names and numbers into the file.

I moved a line on my compiler so now 37 was 38, we are talking about the same error.

I know what you are trying to do here and I really appreciate it. I have a solid understanding in C and C++ and am trying to learn Java on my own. Therefore I understand the diligence required to learn a high level language. I am not here looking for a freebee which I am sure is a common practice around here.

We have established null is the issue. I made the values null in the constructor, didn't work, Tried to make a new object and initialize it, nope didn't work either.

Not liking how vague the errors are in Java.

AS I said I created an new object already and it didn't work either. I even tried to create it in my constructor.

Post 12 has the code.